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    /*
        GRAPH.I
        Declarations of Yorick graphics functions.

        $Id: graph.i,v 1.1 1993/08/27 18:32:09 munro Exp $
     */
    /*    Copyright (c) 1994.  The Regents of the University of California.
                        All rights reserved.  */

    /*--------------------------------------------------------------------------*/
    /* Control functions */

    extern window ;

    /* DOCUMENT window, n, display="host:server.screen", dpi=100/75, wait=0/1,

                           private=0/1, hcp="hcp_filename", dump=0/1,
                           legends=1/0, style="style_sheet_filename",

                           width=wpixels,height=hpixels,rgb=1

         select window N as the current graphics output window.  N may

         range from 0 to 7, inclusive.  Each graphics window corresponds to

         an X window, and optionally has its own associated hardcopy file.
         If N is omitted, it defaults to the current coordinate system.

         The X window will appear on your default display at 75 dpi, unless

         you specify the display and/or dpi keywords.  A dpi=100 X window

         is larger than a dpi=75 X window; both represent the same thing

         on paper.  Use display="" to create a graphics window which has

         no associated X window (you should do this if you want to make

         plots in a non-interactive batch mode).

         By default, if the X window needs to be created, the graphics area

         will be 450x450 pixels if dpi=75, or 600x600 pixels if dpi=100,
         representing a 6x6 inch square on hardcopy paper.  You can override

         this default initial size using the width and height keywords.

         These settings remain in force indefinitely; use width=0,height=0
         to return to the default dpi-dependent behavior.  For a dpi=75,

         landscape=0 window, width=638,height=825 displays the entire sheet
         of hardcopy paper.  Supplying these keywords will not change the

         size of an existing window; only newly created windows.

         By default, an X window will attempt to use shared colors, which
         permits several Yorick graphics windows (including windows from
         multiple instances of Yorick) to use a common palette.  You can

         force an X window to post its own colormap (set its colormap
         attribute) with the private=1 keyword.  You will most likely have

         to fiddle with your window manager to understand how it handles
         colormap focus if you do this.  Use private=0 to return to shared
         colors.

         By default, Yorick will not wait for the X window to become visible;

         code which creates a new window, then plots a series of frames to

         that window should use wait=1 to assure that all frames are actually
         plotted.

         By default, a graphics window does NOT have a hardcopy file
         of its own -- any request for hardcopy are directed to the

         default hardcopy file, so hardcopy output from any window goes

         to a single file.  By specifying the hcp keyword, however, a

         hardcopy file unique to this window will be created.  If the
         "hcp_filename" ends in ".ps", the hardcopy file will be a PostScript
         file; otherwise, hardcopy files are in binary CGM format.  Use

         hcp="" to revert to the default hardcopy file (closing the window
         specific file, if any).  The legends keyword, if present, controls
         whether the curve legends are (legends=1, the default) or are not
         (legends=0) dumped to the hardcopy file.  The dump keyword, if
         present, controls whether all colors are converted to a gray scale,

         (dump=0), or the current palette is dumped at the beginning of each
         page of hardcopy output (dump=1, the default).  (The legends keyword
         applies to all pictures dumped to hardcopy from this graphics
         window.  The dump keyword applies only to the specific hardcopy

         file defined using the hcp keyword -- use the dump keyword in the

         hcp_file command to get the same effect in the default hardcopy
         file.)

         Use rgb=1 to set the rgb color model when you are creating a

         window on an 8-bit display on which you intend to use three

         component rgb colors (see color).  This installs the 5x9x5

         colorcube and avoids having to issue the palette command

         after the first true color object has been drawn.

         If both display="" and hcp="", the graphics window will be
         entirely eliminated.

         The style keyword, if present, specifies the name of a Gist style
         sheet file; the default is "work.gs".  The style sheet determines
         the number and location of coordinate systems, tick and label styles,

         and the like.  Other choices include "axes.gs", "boxed.gs",
         "work2.gs", and "boxed2.gs".

         If invoked as a function, window(...) returns the current
         window number.

       SEE ALSO: plsys, hcp_file, fma, hcp, redraw, palette, animate, plg,

                 winkill, gridxy
     */

    func winkill (n)
    /* DOCUMENT winkill
             or winkill, n

         deletes the current graphics window, or graphics window N (0-7).
       SEE ALSO: window
     */
    {

      window, n, display="", hcp="";
    }

    extern current_window ;

    /* DOCUMENT n= current_window()

         returns the number of the current graphics window, or -1 if none.
     */

    extern hcp_file ;

    /* DOCUMENT hcp_file, filename, dump=0/1, ps=0/1
         sets the default hardcopy file to FILENAME.  If FILENAME ends with
         ".ps", the file will be a PostScript file, otherwise it will be a
         binary CGM file.  By default, the hardcopy file name will be
         "Aa00.cgm", or "Ab00.cgm" if that exists, or "Ac00.cgm" if both
         exist, and so on.  The default hardcopy file gets hardcopy from all
         graphics windows which do not have their own specific hardcopy file

         (see the window command).  If the dump keyword is present and non-zero,

         the current palette will be dumped at the beginning of each frame
         of the default hardcopy file (default behavior).  With dump=0,
         all colors are converted to a gray scale, and the output files are

         smaller because no palette information is included.

         Use ps=1 to make "Aa00.ps", "Ab00.ps", etc by default instead of CGM.
         The dump= and ps= settings persist until explicitly changed by a

         second call to hcp_file; the dump=1 setting becomes the default for
         the window command as well.

       SEE ALSO: window, fma, hcp, plg
     */

    extern hcp_finish ;

    /* DOCUMENT filename= hcp_finish()

             or filename= hcp_finish(n)
         closes the current hardcopy file and returns the filename.

         If N is specified, closes the hcp file associated with window N

         and returns its name; use hcp_finish(-1) to close the default
         hardcopy file.

       SEE ALSO: window, fma, hcp, hcp_out, plg
     */

    func hcp_out (n,keep=)
    /* DOCUMENT hcp_out
             or hcp_out, n
         finishes the current hardcopy file and sends it to the printer.

         If N is specified, prints the hcp file associated with window N;

         use hcp_out,-1 to print the default hardcopy file.
         Unless the KEEP keyword is supplied and non-zero, the file will
         be deleted after it is processed by gist and sent to lpr.

       SEE ALSO: window, fma, hcp, hcp_finish, plg
     */
    {
      filename= hcp_finish();
      if (filename) {

        if (strpart(filename,-2:0)==".ps")

          system, swrite(format=LPR_FORMAT, filename);
        else

          system, swrite(format=GIST_FORMAT, filename);
        if (!keep) remove, filename;
      }
    }

    func hcps (name)
    /* DOCUMENT hcps, name

         writes the picture in the current graphics window to the
         PostScript file NAME+".ps" (i.e.- the suffix .ps is added to NAME).

         Legends are not written, but the palette is always dumped.

       SEE ALSO: hcps, window, fma, hcp, hcp_finish, plg
     */
    {

      if (strpart(name,-2:0)!=".ps") name+= ".ps";

      window, hcp=name, dump=1, legends=0;
      hcp;

      window, hcp="";
      return name;
    }

    func eps (name)
    /* DOCUMENT eps, name

         writes the picture in the current graphics window to the Encapsulated
         PostScript file NAME+".epsi" (i.e.- the suffix .epsi is added to NAME).

         The eps function requires the ps2epsi utility which comes with the
         project GNU Ghostscript program.  Any hardcopy file associated with

         the current window is first closed, but the default hardcopy file is

         unaffected.  As a side effect, legends are turned off and color table
         dumping is turned on for the current window.
         The external variable PS2EPSI_FORMAT contains the format for the
         command to start the ps2epsi program.

       SEE ALSO: hcps, window, fma, hcp, hcp_finish, plg
     */
    {
      name= hcps(name);

      system, swrite(format=PS2EPSI_FORMAT, name);
      remove, name;
    }

    if (is_void(PS2EPSI_FORMAT)) PS2EPSI_FORMAT= "ps2epsi %s";

    extern fma ;
    /* DOCUMENT fma
         frame advance the current graphics window.  The current picture

         remains displayed in the associated X window until the next element
         is actually plotted.

       SEE ALSO: window, hcp, animate, plg
     */

    extern hcp ;

    extern hcpon ;

    extern hcpoff ;
    /* DOCUMENT hcp
                hcpon
    	    hcpoff

         The hcp command sends the picture displayed in the current graphics

         window to the hardcopy file.  (The name of the default hardcopy file

         can be specified using hcp_file; each individual graphics window may

         have its own hardcopy file as specified by the window command.)

         The hcpon command causes every fma (frame advance) command to do

         and implicit hcp, so that every frame is sent to the hardcopy file.

         The hcpoff command reverts to the default "demand only" mode.

       SEE ALSO: window, fma, plg, eps, hcps
     */

    extern redraw ;
    /* DOCUMENT redraw

         redraws the X window associated with the current graphics window.

       SEE ALSO: window, fma, hcp, plg
     */

    extern palette ;
    /* DOCUMENT palette, filename

             or palette, source_window_number

             or palette, red, green, blue, ntsc=1/0

             or palette, red, green, blue, gray

    	 or palette, red, green, blue, query=1

    	 or palette, red, green, blue, gray, query=1

         sets (or retrieves with query=1) the palette for the current

         graphics window.  The FILENAME is the name of a Gist palette file;
         the standard palettes are "earth.gp", "stern.gp", "rainbow.gp",
         "heat.gp", "gray.gp", and "yarg.gp".  Use the maxcolors keyword

         in the pldefault command to put an upper limit on the number of

         colors which will be read from the palette in FILENAME.

         In the second form, the palette for the current window is copied

         from the SOURCE_WINDOW_NUMBER.  If the X colormap for the window is
         private, there will still be two separate X colormaps for the two

         windows, but they will have the same color values.

         In the third form, RED, GREEN, and BLUE are 1-D arrays of the same

         length specifying the palette you wish to install; the values

         should vary between 0 and 255, and your palette should have no
         more than 240 colors.  If ntsc=0, monochrome devices (such as most
         laser printers) will use the average brightness to translate your
         colors into gray; otherwise, the NTSC (television) averaging will
         be used (.30*RED+.59*GREEN+.11*BLUE).  Alternatively, you can specify
         GRAY explicitly.

         Ordinarily, the palette is not dumped to a hardcopy file

         (color hardcopy is still rare and expensive), but you can

         force the palette to dump using the window or hcp_file commands.

         See the dump= keyword for the hcp_file and window commands if you

         are having trouble getting color in your hardcopy files.

       SEE ALSO: window, fma, hcp, pldefault, plg
     */

    extern animate ;
    /* DOCUMENT animate
             or animate, 0/1
         without any arguments, toggles animation mode; with argument 0,
         turns off animation mode, with argument 1 turns on animation mode.

         In animation mode, the X window associated with a graphics window
         is actually an offscreen pixmap which is bit-blitted onscreen

         when an fma command is issued.  This is confusing unless you are

         actually trying to make a movie, but results in smoother animation

         if you are.  Generally, you should turn animation on, run your movie,
         then turn it off.

       SEE ALSO: window, fma, plg
     */

    extern plsys ;
    /* DOCUMENT plsys, n

             or plsys(n)   or   plsys()

         sets the current coordinate system to number N in the current
         graphics window.  If N equals 0, subsequent elements will be
         plotted in absolute NDC coordinates outside of any coordinate
         system.  The default style sheet "work.gs" defines only a single

         coordinate system, so the only other choice is N equal 1.  You

         can make up your own style sheet (using a text editor) which
         defines mulitple coordinate systems.  You need to do this if
         you want to display four plots side by side on a single page,
         for example.  The standard style sheets "work2.gs" and "boxed2.gs"
         define two overlayed coordinate systems with the first labeled

         to the right of the plot and the second labeled to the left of
         the plot.  When using overlayed coordinate systems, it is your

         responsibility to ensure that the x-axis limits in the two
         systems are identical.

         Return value is coordinate system setting before this call;
         input n may be nil to retrieve this without changing it.  Return
         value can be <0 if the information is unavailable for some reason.

       SEE ALSO: window, limits, plg
     */

    /*--------------------------------------------------------------------------*/
    /* Plotting functions (output primitives) */

    extern plg ;
    /* DOCUMENT plg, y, x
             or plg, y
         plots a graph of Y versus X.  Y and X must be 1-D arrays of equal

         length; if X is omitted, it defaults to [1, 2, ..., numberof(Y)].
         A keyword n=[n1,n2,n3,...nN] can be used to add N curves.  In this

         case, sum(n) must be numberof(y).

         The following keywords are legal (each has a separate help entry):

       KEYWORDS: legend, hide

    	     type, width, color, closed, smooth

                 marks, marker, mspace, mphase

    	     rays, arrowl, arroww, rspace, rphase

       SEE ALSO: plg, plm, plc, plv, plf, pli, plt, pldj, plfp, plmk

                 limits, logxy, range, fma, hcp
     */

    extern plm ;

    /* DOCUMENT plm, y, x, boundary=0/1, inhibit=0/1/2

             or plm, y, x, ireg, boundary=0/1, inhibit=0/1/2
    	 or plm, boundary=0/1, inhibit=0/1/2
         plots a mesh of Y versus X.  Y and X must be 2-D arrays with equal

         dimensions.  If present, IREG must be a 2-D region number array
         for the mesh, with the same dimensions as X and Y.  The values of

         IREG should be positive region numbers, and zero for zones which do
         not exist.  The first row and column of IREG never correspond to any
         zone, and should always be zero.  The default IREG is 1 everywhere
         else.  If present, the BOUNDARY keyword determines whether the
         entire mesh is to be plotted (boundary=0, the default), or just the

         boundary of the selected region (boundary=1).  If present, the
         INHIBIT keyword causes the (X(,j),Y(,j)) lines to not be plotted
         (inhibit=1), or the (X(i,),Y(i,)) lines to not be plotted (inhibit=2).
         By default (inhibit=0), mesh lines in both logical directions are
         plotted.
         The Y, X, and IREG arguments may all be omitted to default to the

         mesh set by the most recent plmesh call.

         The following keywords are legal (each has a separate help entry):

       KEYWORDS: legend, hide

    	     type, width, color
    	     region

       SEE ALSO: plg, plm, plc, plv, plf, pli, plt, pldj, plfp, plmesh

                 limits, logxy, range, fma, hcp
     */

    extern plmesh ;

    /* DOCUMENT plmesh, y, x, ireg, triangle=tri_array
             or plmesh

         sets the default mesh for subsequent plm, plc, plv, and plf calls.

         In the second form, deletes the default mesh (until you do this,
         or switch to a new default mesh, the default mesh arrays persist and
         take up space in memory).  The Y, X, and IREG arrays should all be
         the same shape; Y and X will be converted to double, and IREG will
         be converted to int.  If IREG is omitted, it defaults to IREG(1,)=

         IREG(,1)= 0, IREG(2:,2:)=1; that is, region number 1 is the whole

         mesh.  The triangulation array TRI_ARRAY is used by plc; the
         correspondence between TRI_ARRAY indices and zone indices is the
         same as for IREG, and its default value is all zero.
         The IREG or TRI_ARRAY arguments may be supplied without Y and X

         to change the region numbering or triangulation for a given set of
         mesh coordinates.  However, a default Y and X must already have been
         defined if you do this.
         If Y is supplied, X must be supplied, and vice-versa.

       SEE ALSO: plm, plc, plv, plf, plfp
     */

    extern plc ;

    /* DOCUMENT plc, z, y, x, levs=z_values

             or plc, z, y, x, ireg, levs=z_values
    	 or plc, z, levs=z_values
         plots a contours of Z on the mesh Y versus X.  Y, X, and IREG are

         as for plm.  The Z array must have the same shape as Y and X.
         The function being contoured takes the value Z at each point

         (X,Y) -- that is, the Z array is presumed to be point-centered.
         The Y, X, and IREG arguments may all be omitted to default to the

         mesh set by the most recent plmesh call.
         The LEVS keyword is a list of the values of Z at which you want

         contour curves.  The default is eight contours spanning the
         range of Z.

         See plfc if you want to color the regions between contours.

         The following keywords are legal (each has a separate help entry):

       KEYWORDS: legend, hide

    	     type, width, color, smooth

                 marks, marker, mspace, mphase

    	     smooth, triangle, region

       SEE ALSO: plg, plm, plc, plv, plf, pli, plt, pldj, plfp, plmesh, plfc

                 contour, spann, limits, logxy, range, fma, hcp
     */

    extern contour ;

    /* DOCUMENT nc= contour(yc,xc, level, z, y,x)

             or nc= contour(yc,xc, level, z, y,x,ireg)

         returns the points on the contour curve that would have been

         plotted by plc.  Z, Y, X, and IREG are as for plc, and the

         triangle= and region= keywords are accepted and have the same

         meaning as for plc.  Unlike plc, the triangle array is an output

         as well as an input to contour; if supplied it may be modified
         to reflect any triangulations which were performed by contour.

         LEVEL is a scalar z value to return the points at that contour

         level.  All such points lie on edges of the mesh.  If a contour
         curve closes, the final point is the same as the initial point
         (i.e.- that point is included twice in the returned list).

         LEVEL is a pair of z values [z0,z1] to return the points of
         a set of polygons which outline the regions between the two

         contour levels.  These will include points on the mesh boundary
         which lie between the levels, in addition to the edge points

         for both levels.  The polygons are closed, simply connected,
         and will not contain more than about 4000 points (larger polygons

         are split into pieces with a few points repeated where the pieces
         join).

         YC and XC are the output points on the curve(s), or nil if there
         are no points.  On input, they must be simple variable references,
         not expressions.  The return value NC is a list of the lengths of
         the polygons/polylines returned in (XC,YC), or nil if there are

         none.  numberof(XC)==numberof(YC)==sum(NC).  For the level pair
         case, YC, XC, and NC are ready to be used as inputs to plfp.

       KEYWORDS: triangle, region

       SEE ALSO: plc, plfp
     */

    extern plv ;

    /* DOCUMENT plv, vy, vx, y, x, scale=dt

             or plv, vy, vx, y, x, ireg, scale=dt
    	 or plv, vy, vx, scale=dt
         plots a vector field (VX,VY) on the mesh (X,Y).  Y, X, and IREG are
         as for plm.  The VY and VX arrays must have the same shape as Y and X.
         The Y, X, and IREG arguments may all be omitted to default to the

         mesh set by the most recent plmesh call.
         The SCALE keyword is the conversion factor from the units of
         (VX,VY) to the units of (X,Y) -- a time interval if (VX,VY) is a velocity
         and (X,Y) is a position -- which determines the length of the
         vector "darts" plotted at the (X,Y) points.  If omitted, SCALE is
         chosen so that the longest ray arrows have a length comparable
         to a "typical" zone size.

         You can use the scalem keyword in pledit to make adjustments to the
         SCALE factor computed by default.

         The following keywords are legal (each has a separate help entry):

       KEYWORDS: legend, hide

    	     type, width, color, smooth

                 marks, marker, mspace, mphase

    	     triangle, region

       SEE ALSO: plg, plm, plc, plv, plf, pli, plt, pldj, plfp, plmesh, pledit,

                 limits, logxy, range, fma, hcp
     */

    extern plf ;
    /* DOCUMENT plf, z, y, x
             or plf, z, y, x, ireg
    	 or plf, z
         plots a filled mesh Y versus X.  Y, X, and IREG are as for plm.

         The Z array must have the same shape as Y and X, or one smaller

         in both dimensions.  If Z is of type char, it is used "as is",

         otherwise it is linearly scaled to fill the current palette, as
         with the bytscl function.

         (See the bytscl function for explanation of top, cmin, cmax.)

         The mesh is drawn with each zone in the color derived from the Z

         function and the current palette; thus Z is interpreted as a
         zone-centered array.

         As for pli and plfp, Z may also be a 3x(NX-1)x(NY-1) array
         of char giving the [r,g,b] components of each color.  See the

         color keyword for cautions about using this if you do not have
         a true color display.

         The Y, X, and IREG arguments may all be omitted to default to the

         mesh set by the most recent plmesh call.
         A solid edge can optionally be drawn around each zone by setting
         the EDGES keyword non-zero.  ECOLOR and EWIDTH determine the edge

         color and width.  The mesh is drawn zone by zone in order from
         IREG(2+imax) to IREG(jmax*imax) (the latter is IREG(imax,jmax)),
         so you can achieve 3D effects by arranging for this order to
         coincide with back-to-front order.  If Z is nil, the mesh zones

         are filled with the background color, which you can use to
         produce 3D wire frames.

         The following keywords are legal (each has a separate help entry):

       KEYWORDS: legend, hide

    	     region, top, cmin, cmax, edges, ecolor, ewidth

       SEE ALSO: plg, plm, plc, plv, plf, pli, plt, pldj, plfp, plmesh,

                 limits, logxy, range, fma, hcp, palette, bytscl, histeq_scale
     */

    extern plfp ;
    /* DOCUMENT plfp, z, y, x, n
         plots a list of filled polygons Y versus X, with colors Z.

         The N array is a 1D list of lengths (number of corners) of the

         polygons; the 1D colors array Z has the same length as N.  The
         X and Y arrays have length sum(N).

         If Z is of type char, it is used "as is", otherwise it is linearly

         scaled to fill the current palette, as with the bytscl function.

         If Z is nil, the background color is used for every polygon.

         (See the bytscl function for explanation of top, cmin, cmax.)

         As for plf and pli, Z may also be a 3-by-numberof(N) array of
         char giving the [r,g,b] components of each color.  See the

         color keyword for cautions about using this if you do not have
         a true color display.

         As a special case, if n(2:)==1, the first polygon is assumed
         to have NDC coordinates, while the remaining individual X and Y
         values are in world coordinates.  The first polygon is drawn

         numberof(n)-1 times, with its (0,0) placed at each of the
         individual (X,Y) values in succession.  This is a hack to enable

         plotting of more elaborate data markers than plg,type=0 -- see
         the plmk function for details.

         The following keywords are legal (each has a separate help entry):

       KEYWORDS: legend, hide, top, cmin, cmax, edges, ecolor, ewidth

       SEE ALSO: plg, plm, plc, plv, plf, pli, plt, pldj, plfc

                 limits, logxy, range, fma, hcp
     */

    extern pli ;
    /* DOCUMENT pli, z
             or pli, z, x1, y1
             or pli, z, x0, y0, x1, y1

         plots the image Z as a cell array -- an array of equal rectangular

         cells colored according to the 2-D array Z.  The first dimension

         of Z is plotted along x, the second dimension is along y.

         If Z is of type char, it is used "as is", otherwise it is linearly

         scaled to fill the current palette, as with the bytscl function.

         (See the bytscl function for explanation of top, cmin, cmax.)

         As for plf and plfp, Z may also be a 3D array with 1st dimension 3
         of char giving the [r,g,b] components of each color.  See the

         color keyword for cautions about using this if you do not have
         a true color display.

         If X1 and Y1 are given, they represent the coordinates of the
         upper right corner of the image.  If X0, and Y0 are given, they
         represent the coordinates of the lower left corner, which is at

         (0,0) by default.  If only the Z array is given, each cell will be

         a 1x1 unit square, with the lower left corner of the image at (0,0).

         The following keywords are legal (each has a separate help entry):

       KEYWORDS: legend, hide, top, cmin, cmax

       SEE ALSO: plg, plm, plc, plv, plf, pli, plt, pldj, plfp,

                 limits, logxy, range, fma, hcp, palette, bytscl, histeq_scale
     */

    extern pldj ;
    /* DOCUMENT pldj, x0, y0, x1, y1
         plots disjoint lines from (X0,Y0) to (X1,Y1).  X0, Y0, X1, and Y1
         may have any dimensionality, but all must have the same number of
         elements.

         The following keywords are legal (each has a separate help entry):

       KEYWORDS: legend, hide

    	     type, width, color

       SEE ALSO: plg, plm, plc, plv, plf, pli, plt, pldj, plfp

                 limits, logxy, range, fma, hcp
     */

    extern plt ;
    /* DOCUMENT plt, text, x, y, tosys=0/1
         plots TEXT (a string) at the point (X,Y).  The exact relationship
         between the point (X,Y) and the TEXT is determined by the

         justify keyword.  TEXT may contain newline ("\n") characters
         to output multiple lines of text with a single call.  The
         coordinates (X,Y) are NDC coordinates (outside of any coordinate

         system) unless the tosys keyword is present and non-zero, in
         which case the TEXT will be placed in the current coordinate

         system.  However, the character height is NEVER affected by the

         scale of the coordinate system to which the text belongs.

         Note that the pledit command takes dx and/or dy keywords to
         adjust the position of existing text elements.

         The characters ^, _, and ! are treated specially in TEXT.

         ^ begins a superscript, _ begins a subscript, and ! causes the
         following character to be rendered using the symbol font.  As

         special cases, !^, !_, and !! render the ^, _, and ! characters
         themselves.  However, if ! is the final character of TEXT
         (or immediately before a newline in multiline text), it
         loses its special meaning.  TEXT has just three modes: ordinary,
         superscript, and subscript.  A ^ character enters superscript
         mode from ordinary or subscript mode, and returns to ordinary

         mode from superscript mode.  A _ enters subscript mode, except
         from subscript mode it returns to ordinary mode.  For example,
         Euclid said, "!pr^2", and Einstein said, "G_!s!n_=8!pT_!s!n".
         One final special escape: !] produces the ^ character in the

         symbol font (it is a perpendicular sign, whereas ] is just ]).

         The following keywords are legal (each has a separate help entry):

       KEYWORDS: legend, hide

    	     color, font, height, opaque, orient, justify

       SEE ALSO: plt1, plg, plm, plc, plv, plf, pli, plt, pldj, plfp, pledit

                 limits, range, fma, hcp, pltitle
     */

    func plt1 (text, x, y, tosys=, color=,font=,height=,opaque=,orient=,justify=)
    /* DOCUMENT plt1, text, x, y

         same as plt, but TEXT, X, and Y may be arrays to plot multiple
         strings.  The tosys= keyword works as for plt.

       KEYWORDS: color, font, height, opaque, orient, justify
       SEE ALSO: plt
     */
    {

      n= array(0.,dimsof(text,x,y));
      x+= n;
      y+= n;

      text+= array(string,dimsof(n));
      n= numberof(n);
      for (i=1 ; i<=n ; ++i)

        plt,text(i),x(i),y(i),tosys=tosys,color=color,font=font,height=height,

          opaque=opaque,orient=orient,justify=justify;
    }

    func pltitle (title)
    /* DOCUMENT pltitle, title

         Plot TITLE centered above the coordinate system for any of the
         standard Gist styles.  You may want to customize this for other
         plot styles.

       SEE ALSO: plt, xytitles
     */
    {
      port= viewport();

      plt, title, port(zcen:1:2)(1), port(4)+0.02,

        font=pltitle_font, justify="CB", height=pltitle_height;
    }

    func xytitles (xtitle, ytitle, adjust)

    /* DOCUMENT xytitles, xtitle, ytitle

           -or- xytitles, xtitle, ytitle, [deltax,deltay]

         Plot XTITLE horizontally under the viewport and YTITLE vertically
         to the left of the viewport.  If the tick numbers interfere with
         the labels, you can specify the [DELTAX,DELTAY] in NDC units to
         displace the labels.  (Especially for the y title, the adjustment
         may depend on how many digits the numbers on your scale actually
         have.)  Note that DELTAX moves YTITLE and DELTAY moves XTITLE.

         WARNING: There is no easy way to ensure that this type of title
                  will not interfere with the tick numbering.  Interference

    	      may make the numbers or the title or both illegible.

       SEE ALSO: plt, pltitle
     */
    {

      if (is_void(adjust)) adjust= [0.,0.];
      port= viewport();
      if (xtitle && strlen(xtitle))

        plt, xtitle, port(zcen:1:2)(1), port(3)-0.050+adjust(2),

          font=pltitle_font, justify="CT", height=pltitle_height;
      if (ytitle && strlen(ytitle))

        plt, ytitle, port(1)-0.050+adjust(1), port(zcen:3:4)(1),

          font=pltitle_font, justify="CB", height=pltitle_height, orient=1;
    }

    pltitle_height= 18;
    pltitle_font= "helvetica";

    /*--------------------------------------------------------------------------*/

    /* Plot limits and log/linear scaling */

    e= "e";         /* for use with limits and range functions */

    extern limits ;
    /* DOCUMENT limits

             or limits, xmin, xmax, ymin, ymax,
    	            square=0/1, nice=0/1, restrict=0/1
    	 or old_limits= limits()
    	 or limits, old_limits

         In the first form, restores all four plot limits to extreme values.

         In the second form, sets the plot limits in the current coordinate

         system to XMIN, XMAX, YMIN, YMAX, which may be nil or omitted to
         leave the corresponding limit unchanged, a number to fix the
         corresponding limit to a specified value, or the string "e" to

         make the corresponding limit take on the extreme value of the
         currently displayed data.

         If present, the square keyword determines whether limits marked
         as extreme values will be adjusted to force the x and y scales
         to be equal (square=1) or not (square=0, the default).

         If present, the nice keyword determines whether limits will be
         adjusted to nice values (nice=1) or not (nice=0, the default).
         There is a subtlety in the meaning of "extreme value" when one

         or both of the limits on the OPPOSITE axis have fixed values --

         does the "extreme value" of the data include points which
         will not be plotted because their other coordinate lies outside
         the fixed limit on the opposite axis (restrict=0, the default),
         or not (restrict=1)?

         If called as a function, limits returns an array of 5 doubles;
         OLD_LIMITS(1:4) are the current xmin, xmax, ymin, and ymax,
         and int(OLD_LIMITS(5)) is a set of flags indicating extreme

         values and the square, nice, restrict, and log flags.

         In the fourth form, OLD_LIMITS is as returned by a previous

         limits call, to restore the limits to a previous state.

         In an X window, the limits may also be adjusted interactively
         with the mouse.  Drag left to zoom in and pan (click left to zoom
         in on a point without moving it), drag middle to pan, and click
         (and drag) right to zoom out (and pan).  If you click just above

         or below the plot, these operations will be restricted to the
         x-axis; if you click just to the left or right, the operations
         are restricted to the y-axis.  A shift-left click, drag, and

         release will expand the box you dragged over to fill the plot
         (other popular software zooms with this paradigm).  If the
         rubber band box is not visible with shift-left zooming, try
         shift-middle or shift-right for alternate XOR masks.  Such

         mouse-set limits are equivalent to a limits command specifying

         all four limits EXCEPT that the unzoom command can revert to

         the limits before a series of mouse zooms and pans.

         The limits you set using the limits or range functions carry over

         to the next plot -- that is, an fma operation does NOT reset the
         limits to extreme values.

       SEE ALSO: plsys, range, logxy, zoom_factor, unzoom, plg, viewport
     */

    func range (ymin, ymax) { limits,,, ymin, ymax; }
    /* DOCUMENT range, ymin, ymax

         sets the y-axis plot limits in the current coordinate system to
         YMIN, YMAX, which may be nil or omitted to leave the corresponding
         limit unchanged, a number to fix the corresponding limit to a

         specified value, or the string "e" to make the corresponding limit
         take on the extreme value of the currently displayed data.
         Use    limits, xmin, xmin

         to accomplish the same function for the x-axis plot limits.

       SEE ALSO: plsys, limits, logxy, plg
     */

    extern logxy ;
    /* DOCUMENT logxy, xflag, yflag

         sets the linear/log axis scaling flags for the current coordinate
         system.  XFLAG and YFLAG may be nil or omitted to leave the
         corresponding axis scaling unchanged, 0 to select linear scaling,
         or 1 to select log scaling.

       SEE ALSO: plsys, limits, range, plg, gridxy
     */

    extern gridxy ;
    /* DOCUMENT gridxy, flag
             or gridxy, xflag, yflag
         Turns on or off grid lines according to FLAG.  In the first form, both

         the x and y axes are affected.  In the second form, XFLAG and YFLAG
         may differ to have different grid options for the two axes.  In either
         case, a FLAG value of 0 means no grid lines (the default), a value of
         1 means grid lines at all major ticks (the level of ticks which get
         grid lines can be set in the style sheet), and a FLAG value of 2 means
         that the coordinate origin only will get a grid line.  In styles with

         multiple coordinate systems, only the current coordinate system is
         affected.
         The keywords can be used to affect the style of the grid lines.

         You can also turn the ticks off entirely.  (You might want to do this

         to plot your own custom set of tick marks when the automatic tick
         generating machinery will never give the ticks you want.  For example
         a latitude axis in degrees might reasonably be labeled "0, 30, 60,
         90", but the automatic machinery considers 3 an "ugly" number - only

         1, 2, and 5 are "pretty" - and cannot make the required scale.  In
         this case, you can turn off the automatic ticks and labels, and use

         plsys, pldj, and plt to generate your own.)
         To fiddle with the tick flags in this general manner, set the
         0x200 bit of FLAG (or XFLAG or YFLAG), and "or-in" the 0x1ff bits
         however you wish.  The meaning of the various flags is described

         in the file Y_SITE/gist/work.gs.  Additionally, you can use the
         0x400 bit to turn on or off the frame drawn around the viewport.
         Here are some examples:

            gridxy,0x233        work.gs default setting

            gridxy,,0x200       like work.gs, but no y-axis ticks or labels

            gridxy,,0x231       like work.gs, but no y-axis ticks on right

            gridxy,0x62b        boxed.gs default setting

         The three keywords base60=, degrees=, and hhmm= can be used to get
         alternative tick intervals for base 60 systems instead of the

         usual base 10 systems.  The keyword values are 0 to restore the
         default behavior, 1 to set the feature for the x axis, 2 to set it
         for the y axis, and 3 to set it for both axes.  The base60 feature
         allows ticks and labels at multiples of 30 (up to +-3600).  The
         degrees feature causes labels to be printed modulo 360 (so that a
         scale which runs from, say, 90 to 270 will be printed as 90 to 180
         then -180 to -90, mostly for longitude scales).  The hhmm feature
         causes labels to be printed in the form hh:mm (so that, for example,
         150 will be printed as 02:30, mostly for time of day scales).

       KEYWORDS: color, type, width, base60, degrees, hhmm

       SEE ALSO: window, plsys, limits, range, logxy, viewport
     */

    extern zoom_factor ;

    /* DOCUMENT zoom_factor, factor

         sets the zoom factor for mouse-click zoom in and zoom out operations.
         The default FACTOR is 1.5; FACTOR should always be greater than 1.0.

       SEE ALSO: limits, range, unzoom, plg
     */

    extern unzoom ;
    /* DOCUMENT unzoom

         restores limits to their values before zoom and pan operations
         performed interactively using the mouse.
         Use    old_limits=  limits()
                ...
    	    limits, old_limits

         to save and restore plot limits generally.

       SEE ALSO: limits, range, zoom_factor, plg
     */

    /*--------------------------------------------------------------------------*/
    /* Keywords for plotting functions */

    local legend ;

    /* DOCUMENT legend=   plotting keyword

         sets the legend for a plot.  The default legend is a concatentation

         of the strings used in the original plotting command (plg, plm, etc.),

         except for the plt command, which has no default legend.

         Legends are never plotted to the X window; use the plq command to
         see them interactively.  Legends will appear in hardcopy output
         unless they have been explicitly turned off.

       PLOTTING COMMANDS: plg, plm, plc, plv, plf, pli, plt, pldj
       SEE ALSO: hide
     */

    local hide ;
    /* DOCUMENT hide=   plotting keyword

         sets the visibility of a plotted element.  The default is hide=0,

         which means that the element will be visible.  Use hide=1 to remove

         the element from the plot (but not from the display list).

       PLOTTING COMMANDS: plg, plm, plc, plv, plf, pli, plt, pldj
       SEE ALSO: legend
     */

    local type ;
    /* DOCUMENT type=   plotting keyword
         selects line type.  Valid values are the strings "solid", "dash",
         "dot", "dashdot", "dashdotdot", and "none".  The "none" value
         causes the line to be plotted as a polymarker.  You should also

         check the plmk function if you need polymarkers.

         The type value may also be a number; 0 is "none", 1 is "solid",
         2 is "dash", 3 is "dot", 4 is "dashdot", and 5 is "dashdotdot".

       PLOTTING COMMANDS: plg, plm, plc, pldj

       SEE ALSO: width, color, marks, marker, rays, closed, smooth, plmk
     */

    local width ;

    /* DOCUMENT width=   plotting keyword
         selects line width.  Valid values are positive floating point numbers

         giving the line thickness relative to the default line width of one
         half point, width= 1.0.

       PLOTTING COMMANDS: plg, plm, plc, pldj, plv (only if hollow=1)

       SEE ALSO: type, color, marks, marker, rays, closed, smooth
     */

    local color ;

    /* DOCUMENT color=   plotting keyword
         selects line or text color.  Valid values are the strings "bg", "fg",
         "black", "white", "red", "green", "blue", "cyan", "magenta", "yellow",
         or a 0-origin index into the current palette.  The default is "fg".
         Negative numbers may be used instead of the strings: -1 is bg
         (background), -2 is fg (foreground), -3 is black, -4 is white,
         -5 is red, -6 is green, -7 is blue, -8 is cyan, -9 is magenta, and
         -10 is yellow.  (The negative numbers are actually taken modulo
         256, so -1 is also 255, -2 is 254, and so on.)

         A color can also be a triple [r, g, b], with values running from
         0 for dark to 255 for full intensity.  Beware, however, of

         specifying an rgb color (either as a color keyword or to the

         plf, pli, or plfp commands) if your display is not a true color
         display (for example, if it is 8 bits deep or less).  In that

         case, it may switch to a 5x9x5 color cube, which causes a

         significant degradation in quality of rendering with smooth

         color palettes.  Furthermore, the hcp command will not work
         properly for rgb colors if the file is a CGM.  Use the rgb=1

         keyword in the window command to avoid having to re-issue a

         palette command after the first rgb object is drawn (this is

         unnecessary on true color screens).

       PLOTTING COMMANDS: plg, plm, plc, pldj, plt

       SEE ALSO: type, width, marks, marker, mcolor, rays, closed, smooth
     */

    local marks ;

    /* DOCUMENT marks=   plotting keyword

         selects unadorned lines (marks=0), or lines with occasional markers

         (marks=1).  Ignored if type is "none" (indicating polymarkers instead
         of occasional markers).  The spacing and phase of the occasional

         markers can be altered using the mspace and mphase keywords; the

         character used to make the mark can be altered using the marker
         keyword.

       PLOTTING COMMANDS: plg, plc

       SEE ALSO: type, width, color, marker, rays, mspace, mphase, msize, mcolor
     */

    local marker ;

    /* DOCUMENT marker=   plotting keyword
         selects the character used for occasional markers along a polyline,

         or for the polymarker if type is "none".  The special values
         '\1', '\2', '\3', '\4', and '\5' stand for point, plus, asterisk,
         circle, and cross, which are prettier than text characters on output

         to some devices.  The default marker is the next available capital
         letter, 'A', 'B', ..., 'Z'.

       PLOTTING COMMANDS: plg, plc

       SEE ALSO: type, width, color, marks, rays, mspace, mphase, msize, mcolor
     */

    local mspace , mphase, msize, mcolor;

    /* DOCUMENT mspace=   plotting keyword

             or mphase=   plotting keyword

             or msize=    plotting keyword

             or mcolor=   plotting keyword
         selects the spacing, phase, and size of occasional markers placed

         along polylines.  The msize also selects polymarker size if type
         is "none".  The spacing and phase are in NDC units (0.0013 NDC

         equals 1.0 point); the default mspace is 0.16, and the default

         mphase is 0.14, but mphase is automatically incremented for

         successive curves on a single plot.  The msize is in relative

         units, with the default msize of 1.0 representing 10 points.

         The mcolor keyword is the same as the color keyword, but controls

         the marker color instead of the line color.  Setting the color

         automatically sets the mcolor to the same value, so you only

         need to use mcolor if you want the markers for a curve to be a

         different color than the curve itself.

       PLOTTING COMMANDS: plg, plc

       SEE ALSO: type, width, color, marks, marker, rays
     */

    local rays ;
    /* DOCUMENT rays=   plotting keyword

         selects unadorned lines (rays=0), or lines with occasional ray

         arrows (rays=1).  Ignored if type is "none".  The spacing and phase

         of the occasional arrows can be altered using the rspace and rphase
         keywords; the shape of the arrowhead can be modified using the

         arroww and arrowl keywords.

       PLOTTING COMMANDS: plg, plc

       SEE ALSO: type, width, color, marker, marks, rspace, rphase

                 arroww, arrowl
     */

    local rspace , rphase, arroww, arrowl;

    /* DOCUMENT rspace=   plotting keyword

             or rphase=   plotting keyword

             or arroww=   plotting keyword

             or arrowl=   plotting keyword
         selects the spacing, phase, and size of occasional ray arrows
         placed along polylines.  The spacing and phase are in NDC units

         (0.0013 NDC equals 1.0 point); the default rspace is 0.13, and

         the default rphase is 0.11375, but rphase is automatically
         incremented for successive curves on a single plot.

         The arrowhead width, arroww, and arrowhead length, arrowl are
         in relative units, defaulting to 1.0, which translates to an
         arrowhead 10 points long and 4 points in half-width.
       PLOTTING COMMANDS: plg

       SEE ALSO: type, width, color, marks, marker, rays
     */

    local closed , smooth;

    /* DOCUMENT closed=   plotting keyword

             or smooth=   plotting keyword

         selects closed curves (closed=1) or default open curves (closed=0),

         or Bezier smoothing (smooth>0) or default piecewise linear curves

         (smooth=0).  The value of smooth can be 1, 2, 3, or 4 to get
         successively more smoothing.  Only the Bezier control points are

         plotted to an X window; the actual Bezier curves will show up in
         PostScript hardcopy files.  Closed curves join correctly, which

         becomes more noticeable for wide lines; non-solid closed curves
         may look bad because the dashing pattern may be incommensurate
         with the length of the curve.

       PLOTTING COMMANDS: plg, plc (smooth only)

       SEE ALSO: type, width, color, marks, marker, rays
     */

    local font , height, opaque, orient, justify;

    /* DOCUMENT font=     plotting keyword

             or height=   plotting keyword

             or opaque=   plotting keyword

             or orient=   plotting keyword

             or justify=  plotting keyword

         selects text properties.  The font can be any of the strings
         "courier", "times", "helvetica" (the default), "symbol", or
         "schoolbook".  Append "B" for boldface and "I" for italic, so
         "courierB" is boldface Courier, "timesI" is Times italic, and
         "helveticaBI" is bold italic (oblique) Helvetica.  Your X server
         should have the Adobe fonts (available free from the MIT X
         distribution tapes) for all these fonts, preferably at both 75
         and 100 dpi.  Occasionally, a PostScript printer will not be
         equipped for some fonts; often New Century Schoolbook is missing.

         The font keyword may also be an integer: 0 is Courier, 4 is Times,
         8 is Helvetica, 12 is Symbol, 16 is New Century Schoolbook, and
         you add 1 to get boldface and/or 2 to get italic (or oblique).

         The height is the font size in points; 14.0 is the default.
         X windows only has 8, 10, 12, 14, 18, and 24 point fonts, so
         don't stray from these sizes if you want what you see on the

         screen to be a reasonably close match to what will be printed.

         By default, opaque=0 and text is transparent.  Set opaque=1 to

         white-out a box before drawing the text.  The default orient

         (orient=0) is left-to-right text; set orient=1 for text rotated 90

         degrees so it reads upward, orient=2 for 180 degree rotation so

         it is upside down, and orient=3 for 270 degree rotation so it
         reads downward.

         The default text justification, justify="NN" is normal is both
         the horizontal and vertical directions.  Other possibilities
         are "L", "C", or "R" for the first character, meaning left,
         center, and right horizontal justification, and "T", "C", "H",
         "A", or "B", meaning top, capline, half, baseline, and bottom
         vertical justification.  The normal justification "NN" is equivalent
         to "LA".  Common values are "LA", "CA", and "RA" for garden variety
         left, center, and right justified text, with the y coordinate at the
         baseline of the last line in the string presented to plt.  The

         characters labeling the right axis of a plot are "RH", so that the
         y value of the text will match the y value of the corresponding

         tick.  Similarly, the characters labeling the bottom axis of a plot

         are "CT".  The justify= may also be a number, horizontal+vertical,

         where horizontal is 0 for "N", 1 for "L", 2 for "C", or 3 for "R",
         and vertical is 0 for "N", 4 for "T", 8 for "C", 12 for "H",
         16 for "A", or 20 for "B".

       PLOTTING COMMANDS: plt
       SEE ALSO: color
     */

    local region ;

    /* DOCUMENT region=   plotting keyword

         selects the part of mesh to consider.  The region should match one

         of the numbers in the IREG array.  Putting region=0 (the default)

         means to plot the entire mesh, that is, everything EXCEPT region

         zero (non-existent zones).  Any other number means to plot only

         the specified region number; region=3 would plot region 3 only.

       PLOTTING COMMANDS: plm, plc, plv, plf
     */

    local triangle ;

    /* DOCUMENT triangle=   plotting keyword

         sets the triangulation array for a contour plot.  The triangulation

         array must be the same shape as the IREG (region number) array, and
         the correspondence between mesh zones and indices is the same as

         for IREG.  The triangulation array is used to resolve the ambiguity
         in saddle zones, in which the function Z being contoured has two
         diagonally opposite corners high, and the other two corners low.

         The triangulation array element for a zone is 0 if the algorithm is
         to choose a triangulation, based on the curvature of the first

         contour to enter the zone.  If zone (i,j) is to be triangulated
         from point (i-1,j-1) to point (i,j), then TRIANGLE(i,j)=1,
         while if it is to be triangulated from (i-1,j) to (i,j-1), then
         TRIANGLE(i,j)=-1.  Contours will never cross this "triangulation
         line".

         You should rarely need to fiddle with the traingulation array;
         it is a hedge for dealing with pathological cases.
       PLOTTING COMMANDS: plc
     */

    local hollow , aspect;

    /* DOCUMENT hollow=   plotting keyword

             or aspect=   plotting keyword
         set the appearance of the "darts" of a vector field plot.  The

         default darts, hollow=0, are filled; use hollow=1 to get just the

         dart outlines.  The default is aspect=0.125; aspect is the ratio

         of the half-width to the length of the darts.  Use the color

         keyword to control the color of the darts.
       PLOTTING COMMANDS: plv
       SEE ALSO: color
     */

    local edges , ecolor, ewidth;

    /* DOCUMENT edges=   plotting keyword

             or ecolor=   plotting keyword

             or ewidth=   plotting keyword

         set the appearance of zone edges in a filled mesh plot (plf or plfp).

         By default, edges=0, and the zone edges are not plotted.  If

         edges=1, a solid line is drawn around each zone after it is

         filled; the edge color and width are given by ecolor and ewidth,
         which are "fg" and 1.0 by default.
       PLOTTING COMMANDS: plf

       SEE ALSO: color, width
     */

    /*--------------------------------------------------------------------------*/
    /* Inquiry and editing functions */

    extern plq ;
    /* DOCUMENT plq
             or plq, n_element
    	 or plq, n_element, n_contour
    	 or legend_list= plq()

    	 or properties= plq(n_element, n_contour)
         Called as a subroutine, prints the list of legends for the current

         coordinate system (with an "(H)" to mark hidden elements), or prints

         a list of current properties of element N_ELEMENT (such as line type,

         width, font, etc.), or of contour number N_CONTOUR of element number

         N_ELEMENT (which must be contours generated using the plc command).

         Called as a function, returns either the list of legend strings, or a
         list of pointers to the values of the various element properties.
         Elements and contours are both numbered starting with one; hidden
         elements or contours are included in this numbering.

         The PROPERTIES list returned by plq is a list of pointers to the
         relevent properties for the specified graphical element.  Each
         possible property has a particular index in the returned PROPERTIES
         list as follows:

         *PROPERTIES(1)   int([element type (0 for none, 1 for plg, 2 for pldj,

                                             3 for plt, 4 for plm, 5 for plf,

    					 6 for plv, 7 for plc, 8 for pli,
    					 9 for plfp),

                               hide flag])

         *PROPERTIES(2)   string(legend)

         *PROPERTIES(3)   int array, depends on type (names match keywords):

           1 plg:  [color, type, marks, mcolor, marker, rays, closed, smooth]
           2 pldj: [color, type]

           3 plt:  [color, font, path, justify, opaque]

           4 plm:  [color, type, region, boundary, inhibit]

           5 plf:  [region, edges, ecolor]

           6 plv:  [region, color, hollow]

           7 plc:  [region, color, type, marks, mcolor, marker, smooth]
           8 pli:  nil

         *PROPERTIES(4)   double array, depends on type (names match keywords):

           1 plg:  [width, msize, mspace, mphase, rspace, rphase, arrowl, arroww]
           2 pldj: [width]
           3 plt:  [height, x, y]
           4 plm:  [width]
           5 plf:  [ewidth]

           6 plv:  [width, aspect, scale]

           7 plc:  [width, msize, mspace, mphase]
           8 pli:  [x0, x1, y0, y1]

         *PROPERTIES(5)   long array, depends on type (names match arguments):
           1 plg:  [npoints, &x, &y]

           2 pldj: [npoints, &x0, &y0, &x1, &y1]
           3 plt:  [nchars, &text]

           4 plm:  [imax, jmax, &x, &y, &ireg]

           5 plf:  [imax, jmax, &x, &y, &ireg, &colors]

           6 plv:  [imax, jmax, &x, &y, &ireg, &vx, &vy]

           7 plc:  [imax, jmax, &x, &y, &ireg, &z, &triangle, nlevs, &levs]
           8 pli:  [imax, jmax, &colors]

           9 plfp: [n, &x, &y, &colors, &pn]

         You can use the reshape function to peek at the data at the addresses
         returned in PROPERTIES(5) as longs.  The appropriate data types are:

         char for text, int for ireg, short for triangle, char for colors, and

         double for everything else.  In a plf, colors is (imax-1)-by-(jmax-1).
         Although PROPERTIES(5) returns pointers to the data plotted, attempting
         to poke new values into this data will not produce immediate changes

         to your plot, since the graphics package does not realize that anything

         has changed.  Use pledit to make changes to plotted elements.

         The plq function always operates on the current coordinate system

         in the current graphics window; use window and plsys to change these.

       SEE ALSO: window, plsys, pledit, pldefault, plg
     */

    extern pledit ;

    /* DOCUMENT pledit, key1=value1, key2=value2, ...

             or pledit, n_element, key1=value1, key2=value2, ...

             or pledit, n_element, n_contour, key1=value1, key2=value2, ...

         changes some property of element number N_ELEMENT (and contour
         number N_CONTOUR of that element).  If N_ELEMENT and N_CONTOUR are
         omitted, the default is the most recently added element, or the

         element specified in the most recent plq query command.

         The keywords can be any of the keywords that apply to the current
         element.  These are:

           plg:  color, type, width,

                 marks, mcolor, marker, msize, mspace, mphase,

    	     rays, rspace, rphase, arrowl, arroww,

    	     closed, smooth

           pldj: color, type, width

           plt:  color, font, height, path, justify, opaque

           plm:  region, boundary, inhibit, color, type, width

           plf:  region

           plv:  region, color, hollow, width, aspect, scale

           plc:  region, color, type, width,

                 marks, mcolor, marker, msize, mspace, mphase
    	     smooth, levs
         (For contours, if you aren't talking about a particular N_CONTOUR,
          any changes will affect ALL the contours.)

         A plv (vector field) element can also take the scalem
         keyword to multiply all vector lengths by a specified factor.

         A plt (text) element can also take the dx and/or dy
         keywords to adjust the text position by (dx,dy).

       SEE ALSO: window, plsys, plq, pldefault, plg
     */

    extern pldefault ;

    /* DOCUMENT pldefault, key1=value1, key2=value2, ...
         sets default values for the various properties of graphical elements.

         The keywords can be most of the keywords that can be passed to the
         plotting commands:

           plg:  color, type, width,

                 marks, mcolor, msize, mspace, mphase,

    	     rays, rspace, rphase, arrowl, arroww

           pldj: color, type, width

           plt:  color, font, height, path, justify, opaque

           plm:  color, type, width

           plv:  color, hollow, width, aspect

           plc:  color, type, width,

                 marks, mcolor, marker, msize, mspace, mphase

           plf:  edges, ecolor, ewidth

         The initial default values are:

           color="fg", type="solid", width=1.0 (1/2 point),

           marks=1, mcolor="fg", msize=1.0 (10 points),

              mspace=0.16, mphase=0.14,

           rays=0, arrowl=1.0 (10 points), arroww=1.0 (4 points),

              rspace=0.13, rphase=0.11375,

           font="helvetica", height=12.0, justify="NN", opaque=0,

           hollow= 0, aspect=0.125,

           edges=0, ecolor="fg", ewidth=1.0 (1/2 point)

         Additional default keywords are:

           dpi, style, legends  (see window command)

           palette              (to set default filename as in palette command)
           maxcolors            (default 200)

       SEE ALSO: window, plsys, plq, pledit, plg
     */

    /*--------------------------------------------------------------------------*/
    /* Miscellany */

    extern bytscl ;
    /* DOCUMENT bytscl(z)

             or bytscl(z, top=max_byte, cmin=lower_cutoff, cmax=upper_cutoff)

         returns a char array of the same shape as Z, with values linearly

         scaled to the range 0 to one less than the current palette size.
         If MAX_BYTE is specified, the scaled values will run from 0 to
         MAX_BYTE instead.
         If LOWER_CUTOFF and/or UPPER_CUTOFF are specified, Z values outside

         this range are mapped to the cutoff value; otherwise the linear
         scaling maps the extreme values of Z to 0 and MAX_BYTE.

       SEE ALSO: plf, pli, histeq_scale
     */

    extern mesh_loc ;
    /* DOCUMENT mesh_loc(y0, x0)

             or mesh_loc(y0, x0, y, x)

             or mesh_loc(y0, x0, y, x, ireg)
         returns the zone index (=i+imax*(j-1)) of the zone of the mesh

         (X,Y) (with optional region number array IREG) containing the
         point (X0,Y0).  If (X0,Y0) lies outside the mesh, returns 0.

         Thus, eg- ireg(mesh_loc(x0, y0, y, x, ireg)) is the region number of

         the region containing (x0,y0).  If no mesh specified, uses default.
         X0 and Y0 may be arrays as long as they are conformable.

         For mesh_loc wrappers to duplicate the functionality of the

         digitize and interp functions in 2D, see the library file digit2.i.

         After #include "digit2.i", type:  help,digit2

       SEE ALSO: plmesh, moush, mouse
     */

    extern mouse ;

    /* DOCUMENT result= mouse(system, style, prompt)

         displays a PROMPT, then waits for a mouse button to be pressed,

         then released.  Returns array of eleven doubles:
           result= [x_pressed, y_pressed, x_released, y_released,
                    xndc_pressed, yndc_pressed, xndc_released, yndc_released,
    	        system, button, modifiers]

         If SYSTEM>=0, the first four coordinate values will be relative to
         that coordinate system.
         For SYSTEM<0, the first four coordinate values will be relative to

         the coordinate system under the mouse when the button was pressed.

         The second four coordinates are always normalized device coordinates,
         which start at (0,0) in the lower left corner of the 8.5x11 sheet of

         paper the picture will be printed on, with 0.0013 NDC unit being
         1/72.27 inch (1.0 point).  Look in the style sheet for the location

         of the viewport in NDC coordinates (see the style keyword).

         If STYLE is 0, there will be no visual cues that the mouse
         command has been called; this is intended for a simple click.
         If STYLE is 1, a rubber band box will be drawn; if STYLE is 2,
         a rubber band line will be drawn.  These disappear when the
         button is released.

         Clicking a second button before releasing the first cancels the

         mouse function, which will then return nil.

         Ordinary text input also cancels the mouse function, which again
         returns nil.

         The left button reverses forground for background (by XOR) in
         order to draw the rubber band (if any).  The middle and right
         buttons use other masks, in case the rubber band is not visible
         with the left button.

         long(result(9)) is the coordinate system in which the first four
         coordinates are to be interpreted.
         long(result(10)) is the button which was pressed, 1 for left, 2
         for middle, and 3 for right (4 and 5 are also possible).
         long(result(11)) is a mask representing the modifier keys which
         were pressed during the operation: 1 for shift, 2 for shift lock,
         4 for control, 8 for mod1 (alt or meta), 16 for mod2, 32 for mod3,
         64 for mod4, and 128 for mod5.

       SEE ALSO: moush
     */

    func moush (y, x, ireg)
    /* DOCUMENT moush()
             or moush(y, x, ireg)
         returns the 1-origin zone index for the point clicked in

         for the default mesh, or for the mesh (X,Y) (region array IREG).
     */
    {

      xy= mouse(-1, 0, "<Click mouse in mesh>");
      if (is_void(xy)) return [];

      else return mesh_loc(xy(2), xy(1), y, x, ireg);
    }

    extern pause ;
    /* DOCUMENT pause, milliseconds

         pause for the specified number of milliseconds of wall clock
         time, or until input arrives from the keyboard.
         This is intended for use in creating animated sequences.
     */

    extern rgb_read ;
    /* DOCUMENT rgb = rgb_read()
             or rgb = rgb_read(n)

         Read contents of current graphics window, or of graphics window N.

         RGB is a 3xNXxNY array of char where NXxNY is the current shape of

         the window in pixels.  RGB(1,,) is the red component, RGB(2,,) is
         the green component, and RGB(3,,) is the blue component, with 0
         black and 255 full intensity.  RGB(,,1) is the top row of the

         window, RGB(,,2) the second row, and so on to RGB(,,0), which is

         the bottom row.  (So RGB(,,::-1) to pli redraws a copy.)
     */

    /*--------------------------------------------------------------------------*/

    func histeq_scale (z, top=, cmin=, cmax=)

    /* DOCUMENT histeq_scale(z, top=top_value, cmin=cmin, cmax=cmax)

         returns a byte-scaled version of the array Z having the property

         that each byte occurs with equal frequency (Z is histogram

         equalized).  The result bytes range from 0 to TOP_VALUE, which

         defaults to one less than the size of the current palette (or

         255 if no pli, plf, or palette command has yet been issued).

         If non-nil CMIN and/or CMAX is supplied, values of Z beyond these
         cutoffs are not included in the frequency counts.

       SEE ALSO: bytscl, plf, pli
     */
    {

      if (is_void(top)) top= bytscl([0.,1.])(2);  /* palette size - 1 */
      top= long(top);

      if (top<0 | top>255) error, "top value out of range 0-255";
      y= z(*);

      if (!is_void(cmin)) y= y(where(y>=cmin));

      if (!is_void(cmax)) y= y(where(y<=cmax));
      y= y(sort(y));

      x= span(0.,1., numberof(y));
      xp= span(0.,1., top+2);
      bins= interp(y, x, xp);
      list= where(bins(dif)<=0.0);
      if (numberof(list)) {
        /* some value (or values) of z are repeated many times --
           try to handle this by adding a small slope to the sorted y */
        dy= y(0)-y(1);
        if (!dy) dy= 1.0;

        for (eps=1.e-10 ; eps<1000.1 ; eps*=10.) {

          bins= interp(y+eps*dy*x, x, xp);
          list= where(bins(dif)<=0.0);
          if (!numberof(list)) break;
        }

        if (eps>1000.) error, "impossible error??";
      }

      return char(max(min(digitize(z,bins)-2,top),0));
    }

    /*--------------------------------------------------------------------------*/

    extern viewport ;
    /* DOCUMENT port= viewport();

         returns [xmin,xmax,ymin,ymax] of the current viewport (or 0,0,0,0

         if currently plotting to system 0) in NDC coordinates.

       SEE ALSO: limits, gridxy
     */

    extern raw_style ;

    /* DOCUMENT raw_style: get_style, set_style, read_style, write_style
                #include "style.i"

         alternatives to the style= keyword of the window command which
         allow the interpreter to set or get all the details of the

         window style.  Include "style.i" and read the help for get_style.
     */

    /*--------------------------------------------------------------------------*/

    extern _pl_init ;
    /* xxDOCUMENT _pl_init
         initializes the Gist graphics package -- DON'T EVER CALL THIS.
     */

    _pl_init, GISTPATH; /* ...except right here (see paths.i) */

    extern keybd_focus ;

    /* DOCUMENT keybd_focus, on_off

         By default, graphics windows set a window manager hint which
         allows them to accept keyboard focus.  With ON_OFF zero, that

         hint will not be set when a new graphics window is created.

         This causes the window manager to refuse to offer keyboard

         focus to the graphics window -- very desirable, since it can't
         accept keyboard input anyway.  With fvwm, for example, this

         means keyboard focus can stay in the terminal window even when

         you are mouse zooming the graphics window.  However, many

         window managers confuse colormap focus with keyboard focus, so

         if you set the private=1 colormap in the window function, you

         may not be able to convince the window manager to give the

         graphics window colormap focus since it won't give it keyboard
         focus.  Weird.
     */

    /*--------------------------------------------------------------------------*/

    /* functions which call plg, plf, or other automatic legend generating

     * functions must be defined after _pl_init, since that function turns
     * on argument "quining" which changes the way things are parsed (yuck) */

    func plmk (y,x,marker=,width=,color=,msize=)
    /* DOCUMENT plmk, y,x

         Make a scatter plot of the points Y versus X.  If X is nil,

         it defaults to indgen(numberof(Y)).  By default, the marker

         cycles through 7 predefined marker shapes.  You may specify a shape

         using the marker= keyword, line width using the width= keyword (you

         get solid fills for width>=10), color using the color= keyword.

         You can also use the msize= keyword to scale the marker (default

         msize=1.0).  You can change the default width, color, or msize

         using the plmk_default function.

         The predefined marker= values are:

         marker=
           1	square
           2	cross
           3	triangle
           4	circle
           5	diamond
           6	cross (rotated 45 degrees)
           7	triangle (upside down)

         You may also put marker=[xm,ym] where xm and ym are vectors

         of NDC coordinates to design your own custom marker shapes.

       SEE ALSO: plmk_default, plg (type=0 keyword)
     */
    {

      if (is_void(marker)) {
        marker= (_plmk_count-1)%7 + 1;
        _plmk_count++;
      }

      if (numberof(marker)==1) {

        marker= *_plmk_markers(marker);

      } else if (dimsof(marker)(1)!=2 || dimsof(marker)(3)!=2 ||

    	     dimsof(marker)(2)<=2) {

        error, "illegal marker= keyword value";
      }
      xm= marker(,1);
      ym= marker(,2);

      if (is_void(msize)) msize= _plmk_msize;

      if (!is_void(msize)) {
        xm*= msize;
        ym*= msize;
      }

      if (is_void(color)) color= _plmk_color;

      if (structof(color)==string) {

        n= where(color==["bg","fg","black","white",
    		     "red","green","blue","cyan","magenta","yellow"]);

        if (numberof(n)!=1) error, "unrecognized color name: "+color;
        color= char(-n(1));
      }

      ecolor= color;

      if (is_void(width)) width= _plmk_width;

      if (!is_void(width)) {
        if (width>=10) {
          solid= 1;

          if (is_void(color)) color= ecolor= char(-2);

          z= array(char(color), 1+numberof(y));
          width= [];
        }
      }

      n= array(1,1+numberof(y));
      n(1)= numberof(ym);

      if (is_void(x)) x= indgen(numberof(y));

      plfp, z,grow(ym,y),grow(xm,x),n,edges=1,ewidth=width,ecolor=ecolor;
    }

    func plmk_default (color=, msize=, width=)

    /* DOCUMENT plmk_default, color=color, msize=msize, width=width

         sets default color, msize, and width values for plmk.  Use

         width=10 to get solid fills.  With no parameters, plmk_default
         restores the initial default values.

       SEE ALSO: plmk
     */
    {
      { extern _plmk_color, _plmk_width, _plmk_msize; }
      i= 0;

      if (!is_void(color)) _plmk_color= color;
      else i++;

      if (!is_void(width)) _plmk_width= width;
      else i++;

      if (!is_void(msize)) _plmk_msize= msize;
      else i++;
      if (i==3) _plmk_msize= _plmk_color= _plmk_width= [];
    }

    _plmk_count= 1;
    _plmk_msize= _plmk_color= _plmk_width= [];
    /* predefined markers: square, +, delta, circle, diamond, x, grad */

    _plmk_markers= span(-pi,pi,37)(zcen);
    _plmk_markers= [&([[-1,1,1,-1],[-1,-1,1,1]]*.007),
    	        &([[-4,-1,-1,1,1,4,4,1,1,-1,-1,-4],

    		   [-1,-1,-4,-4,-1,-1,1,1,4,4,1,1]]*.007/sqrt(7)),

    	        &([[-sqrt(3),sqrt(3),0],[-1,-1,2]]*.007/sqrt(.75*sqrt(3))),

    	        &([cos(_plmk_markers),sin(_plmk_markers)]*.007/(pi/4.)),

                    &([[-1,0,1,0],[0,-1,0,1]]*.007*sqrt(2)),
                    &([[-1,-2.5,-1.5,0,1.5,2.5,1,2.5,1.5,0,-1.5,-2.5],
    		   [0,-1.5,-2.5,-1,-2.5,-1.5,0,1.5,2.5,1,2.5,1.5]]*.007*

    		  sqrt(2)/sqrt(7)),

    	        &([[0,sqrt(3),-sqrt(3)],[-2,1,1]]*.007/sqrt(.75*sqrt(3)))];

    func plfc (z, y, x, ireg, levs=, colors=, region=, triangle=)

    /* DOCUMENT plfc, z, y, x, levs=z_values

             or plfc, z, y, x, ireg, levs=z_values

         fills contours of Z on the mesh Y versus X.  Y, X, and IREG are

         as for plm.  The Z array must have the same shape as Y and X.
         The function being contoured takes the value Z at each point

         (X,Y) -- that is, the Z array is presumed to be point-centered.

         The LEVS keyword is a list of the values of Z at which you want

         contour curves.  These curves divide the mesh into numberof(LEVS)+1
         regions, each of which is filled with a solid color.  If LEVS is
         nil, up to 19 "nice" equally spaced level values spanning the

         range of Z are selected.  The level values actually used are
         always output to the external variable plfc_levs.

         If you specify levs=, you may also specify colors= a list of

         colors of length numberof(LEVS)+1.  The colors should be indices
         into the current palette.  If you do not specify them, equally
         spaced colors are chosen.

         The following keywords are legal (each has a separate help entry):

       KEYWORDS: triangle, region

       SEE ALSO: plg, plm, plc, plv, plf, pli, plt, pldj, plfp, plmesh

                 color_bar, spann, contour, limits, logxy, range, fma, hcp
     */
    {
      zmin= min(z);
      zmax= max(z);
      if (is_void(levs)) {

        levs= spann(zmin, zmax, 20, fudge=-0.05);
      } else if (numberof(levs)>1) {
        dz= levs(dif); /* blows up if <2 or not numeric */
        reverse= max(dz);

        if (numberof(dz)!=numberof(levs)-1 ||
    	anyof((dz>0.)!=(reverse>0.)) || !reverse)

          error, "levs= values must be monotone 1D";
        reverse= reverse<0.;
        if (reverse) levs= levs(0:1:-1);
        else levs= levs(1:0);
      } else {
        levs= [double(levs(1))];
      }
      { extern plfc_levs, plfc_colors; }
      plfc_levs= levs;
      n= numberof(levs);

      pairs= [grow([min(-1.e30,1.1*zmin)],levs),
    	  grow(levs,[max( 1.e30,1.1*zmax)])];
      if (reverse) pairs= pairs(0:1:-1,);

      /* make sure some kind of reasonable palette is installed */
      { local nc, yc, xc; }
      palette, query=1, nc, yc, xc;
      nc= numberof(nc);
      if (nc<3) {
        palette, "earth.gp";
        palette, query=1, nc, yc, xc;
        nc= numberof(nc);
      }

      if (is_void(colors)) {

        colors= char(span(0,nc-1,n+2)(zcen));
      } else {
        if (numberof(colors)!=n+1)

          error, "colors= must specify one more color than levs=";
        if (structof(colors)!=char) {
          cmin= min(colors);
          cmax= max(colors);
          dz= 0.5*(cmax-cmin)/double(n+1);

          colors= bytscl(colors,cmin=cmin-dz,cmax=cmax+dz);
        }
      }
      plfc_colors= colors;

      if (is_void(triangle)) triangle= array(short,dimsof(z));

      for (i=1 ; i<=n+1 ; ++i) {
        pair= pairs(i,);
        if (pair(2)<zmin || pair(1)>zmax) continue;

        nc= contour(yc,xc, pair,z,y,x,ireg,triangle=triangle);
        if (!numberof(nc)) continue;

        plfp,array(colors(i),numberof(nc)),yc,xc,nc,edges=0;
      }
    }

    func spann (zmin, zmax, n, fudge=)
    /* DOCUMENT spann(zmin, zmax, n)
         return no more than N equally spaced "nice" numbers between
         ZMIN and ZMAX.

       SEE ALSO: span, spanl, plc, plfc
     */
    {
      if (is_void(fudge)) fudge=
      reverse= zmin>zmax;
      if (reverse) { dz=zmin; zmin=zmax; zmax=dz; }
      dz= (zmax-zmin)/max(double(n),0.);
      if (!dz) dz= abs(zmin);
      if (dz) {

        power= floor(log10(dz)+0.00001);
        base= dz/10.^power;
        if (base>5.00001) { base= 1.0; power+= 1.0; }
        else if (base>2.00001) base= 5.0;
        else base= 2.0;
        /* round dz up to the nearest "nice" number */
        dz= base*10.^power;
        zmin= ceil(zmin/dz - fudge);
        zmax= floor(zmax/dz + fudge);
        nz= long(zmax-zmin+1.0);
        if (nz>1) {
          levs= span(zmin*dz, zmax*dz, nz);
        } else {
          if (nz<1) {   /* find any nice number in interval */
    	if (base<1.5) { base= 5.0; power-= 1.0; }
    	else if (base<2.5) base= 1.0;
    	else base= 2.0;
    	dz= base*10.^power;
    	zmin= ceil(zmin/dz + 0.001);
          }
          levs= [zmin*dz];
        }
      } else {
        levs= [-1.0,1.0];
      }
      if (reverse) levs= levs(0:1:-1);
      return levs;
    }

    func color_bar (levs, colors, vert=, labs=, adjust=, ecolor=)
    /* DOCUMENT color_bar

             or color_bar, levs, colors

         Draw a color bar below the current coordinate system.  If LEVS is

         not specified uses plfc_levs (set by previous call to plfc).  If
         COLORS is specified, it should have one more value than LEVS,
         otherwise equally spaced colors are chosen, or plfc_colors if

         plfc_levs was used.  With the vert=1 keyword the color bar appears

         to the left of the current coordinate system (vert=0 is default).

         By default, color_bar will attempt to label some of the color
         interfaces.  With the labs= keyword, you can force the labelling
         algorithm as follows: labs=0 supresses all labels, labs=n forces
         a label at every nth interface, labs=[i,n] forces a label at every

         nth interface starting from interface i (0<=i<=numberof(LEVS)).
         You can use the adjust= keyword to move the bar closer to (adjust<0)

         or further from (adjust>0) the viewport, and the height= keyword to

         set the height of any labels (default 14 points).
       SEE ALSO: plfc
     */
    {
      if (is_void(levs)) {

        if (is_void(plfc_levs)) error, "no levels specified";
        levs= plfc_levs;
        n= numberof(levs)+1;

        if (is_void(colors)) colors= plfc_colors;
      } else {
        n= numberof(levs)+1;

        if (is_void(colors)) colors= bytscl(span(1,n,n),cmin=0.5,cmax=n+0.5);
      }
      if (n != numberof(colors))

        error, "numberof(colors) must be one more than numberof(levs)";

      port= viewport();
      if (is_void(adjust)) adjust= 0.;
      dx= dy= 0.;
      if (vert) {
        x= (port(2)+adjust+[0.022,0.042])(-:1:n+1,);
        dx= 0.005;

        y= span(port(3),port(4),n+1)(,-:1:2);
      } else {
        y= (port(3)-adjust-[0.045,0.065])(-:1:n+1,);
        dy= -0.005;

        x= span(port(1),port(2),n+1)(,-:1:2);
      }
      sys= plsys(0);

      plf,[colors],y,x,edges=1,ecolor=ecolor, legend="";
      plsys, sys;

      if (is_void(labs) || labs(0)>0) {
        if (numberof(levs)>1) {
          dz= levs(dif);

          if (numberof(dz)!=numberof(levs)-1 ||

    	  anyof((dz>0.)!=(dz(1)>0.)) || !dz(1))
    	error, "levs must be monotone 1D";
          levs= levs(1:0);

          levs= grow([2*levs(1)-levs(2)],levs,[2*levs(0)-levs(-1)]);
        } else {
          levs= double(levs(1));
          if (!levs) levs= [-1.,levs,1.];
          else levs= [0.,levs,2*levs];
        }
        if (numberof(labs)<2) {

          if (is_void(labs)) labs= (n-1)/4 + 1;

          orig= where(levs<1.e-9*max(levs(dif)));

          if (numberof(orig)==1) labs= [orig(1)%labs,labs];
          else labs= [(n%labs)/2,labs];
        }

        list= where(indgen(0:n)%labs(2)==labs(1));
        x= x(list,);
        y= y(list,);

        labs= swrite(format="%g",levs(list));
        plsys, 0;

        pldj, x(,2),y(,2),x(,2)+dx,y(,2)+dy, legend="";
        plsys, sys;

        plt1, labs,x(,2)+dx,y(,2)+dy, justify=(vert?"LH":"CT"), height=height,
          font="helvetica";
      }
    }

    /*--------------------------------------------------------------------------*/