# Grace User's Guide (v0.3)

## by the Grace Team

22.08.1999

This document explains the usage of Grace, a 2D plotting tool for scientific data.

## 1. Introduction

## 1.1 What is Grace?

Grace is a WYSIWYG tool to make two-dimensional plots of scientific data. It runs under various (if not all) flavors of Unix with X11 and Motif (LessTif). It also runs under VMS, OS/2, and Windows (95/98/NT). Its capabilities are roughly similar to GUI-based programs like Sigmaplot or Microcal Origin plus script-based tools like Gnuplot or Genplot. Its strength lies in the fact that it combines the convenience of a graphical user interface with the power of a scripting language which enables it to do sophisticated calculations or perform automated tasks.

Grace is derived from Xmgr (a.k.a. ACE/gr), originally written by Paul Turner.

From version number 4.00, the development was taken over by a team of volunteers under the coordination of Evgeny Stambulchik. You can get the newest information about Grace and download the latest version at the Grace home page.

When its copyright was changed to GPL, the name was changed to Grace, which stands for ``GRaphing, Advanced Computation and Exploration of data'' or ``Grace Revamps ACE/gr''. The first version of Grace available is named 5.0.0, while the last public version of Xmgr has the version number 4.1.2.

Paul still maintains and develops a non-public version of Xmgr for internal use.

## 1.2 Copyright statement

> `

>     Copyright (©) 1991-95 Paul J Turner, Portland, OR
>     Copyright (©) 1996-99 Grace Development Team

>     Maintained by Evgeny Stambulchik

>                              All Rights Reserved

>     This program is free software; you can redistribute it and/or modify
>     it under the terms of the GNU General Public License as published by
>     the Free Software Foundation; either version 2 of the License, or
>     (at your option) any later version.

>     This program is distributed in the hope that it will be useful,
>     but WITHOUT ANY WARRANTY; without even the implied warranty of
>     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>     GNU General Public License for more details.

>     You should have received a copy of the GNU General Public License
>     along with this program; if not, write to the Free Software
>     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

> `

## 1.3 Comments and bug reports

## 2. Installation guide

## 2.1 Installing from sources

1. Configuration
   - Extra libraries. Some features will be available only if additional libraries are installed. Those are:
     - The PDF driver requires the PDFlib-2.01 library of Thomas Merz to be installed, which is available here.
     - The JPEG backend needs the IJG's ( JPEG library).
     - The PNG backend needs the ( libpng) library.
     - If your computer has the FFTW library installed when Grace is compiled, Grace will link itself to this, and drop all conventional FFT's and DFT's. All transforms will be routed through this package. Note that there is then no difference between pushing the "FFT" button and the "DFT" button, except that FFT will complain if the length isn't a power of 2, and DFT will not. For more information on this package, see the FFTW Home page. In short, this package allows one to do non-power-of-2 length FFT's along with the normal ones. It seems to work very efficiently for any set length which factors into 2^a 3^b 5^c 7^d for integer a, b, c, d. The great feature here is that set lengths which are powers of 10 (e.g. 1000, 10000) and integer multiples of these (500, 2000, 2500, 5000, etc.) can be computed with no significant penalty (maybe 20%) over power-of-2 transforms. Very often, real datasets come in these sizes, and not in powers of 2.
     - In order to read/write sets in the NetCDF data format, you will also need the NetCDF libraries.
   - Consult README.configure for basic notes on the GNU configure usage
   - Run `./configure --help` to get list of additional switches specific to Grace
   - Run `./configure <options>`. Just an example:

           % ./configure --enable-grace-home=/opt/grace
           --enable-extra-incpath=/usr/local/include:/opt/include \
           --enable-extra-ldpath=/usr/local/lib:/opt/lib --prefix=/usr

     would use `/usr/local/include` and `/opt/include` in addition to the default include path and `/usr/local/lib` and `/opt/lib` in addition to the default ld path. As well, all stuff would be put under the /opt/grace directory and soft links made to `/usr/bin`, `/usr/lib` and `/usr/include`.

     Note: If you change one of the `--enable-extra-incpath` or `--enable-extra-ldpath` options from one run of configure to another, remember to delete the `config.cache` file!!!

2. Compilation
   - Issue `make`

     If something goes wrong, try to see if the problem has been described already in the Grace FAQ (in the `doc` directory).

3. Testing
   - `make tests`
4. Installation
   - `make install`
   - `make links`

     The later (optional) step will make soft links from some files under the Grace home directory to the system-wide default locations (can be changed by the `--prefix` option during the configuration, see above).

## 2.2 Binary installation

1. Getting pre-built packages
2. Installation
3. Running tests

## 2.3 Alternative packaging schemes (RPM, ...)

Not written yet...

## 3. Getting started

For a jump-in start, you can browse the demos ("Help/Examples" menu tree). Also, read the Tutorial.

## 3.1 General concepts

### Project files

A project file contains all information necessary to restore a plot created by Grace, as well as some of preferences. Each plot is represented on a single page, but may have an unlimited number of graphs.

### Graphs

A graph consists of (every element is optional): a graph frame, axes, a title and a subtitle, a number of sets and additional annotative objects (time stamp string, text strings, lines, boxes and ellipses).

### Sets

A set is a way of representing numerical data (datasets). It consists of a pointer to a dataset plus a collection of parameters describing the visual appearance of the data (like color, line dash pattern etc).

### Datasets

A dataset is a collection of points with x and y coordinates, up to four optional data values (which, depending on the set type, can be displayed as error bars or like) and one optional character string.

### Regions

Regions are sections of the graph defined by the interior or exterior of a polygon, or a half plane defined by a line. Regions are used to restrict data transformations to a geometric area occupied by region.

### Real Time Input

Real Time Input refers to the ability Grace has to be fed in real time by an external program. The Grace process spawned by the driver program is a full featured Grace process: the user can interact using the GUI at the same time the program sends data and commands. The process will adapt itself to the incoming data rate.

### Hotlinks

Hotlinks are sources containing varying data. Grace can be instructed a file or a pipe is a hotlink in which case it will provide specific commands to refresh the data on a mouse click (a later version will probably allow automatic refresh).

### File formats

Grace understands several input files formats. The most basic one is ASCII text files containing space and comma separated columns of data. The data fields can be either numeric (Fortran 'd' and 'D' exponent markers are supported) or alphanumeric (with or without quotes). Several calendar date formats are recognized automatically and you can specify your own reference for numeric dates formats. Grace also has a command language (see command interpreter), you can include commands in data files using lines having "@" as their first non-blank character. Depending on configuration, Grace can also read NetCDF files (see configuration).

### Devices

Grace allows the user to choose between several output devices to produce its graphics. The current list of supported devices is:

- X11
- PostScript (level 1 and level 2)
- EPS
- Metafile (which is Grace format, used at the moment mostly for debugging purposes)
- PDF (depends on extra libraries, see configuration)
- PNM
- JPEG (depends on extra libraries, see configuration)
- PNG (depends on extra libraries, see configuration)

Note that Grace no longer supports GIF due to the copyright policy of Unisys. Grace can also be instructed to launch conversion programs automatically based on file name. As an example you can produce MIF (FrameMaker Interchange Format) or Java applets using pstoedit, or almost any image format using the netpbm suite (see the FAQ).

### Magic path

In many cases, when Grace needs to access a file given with a relative `pathname`, it searches for the file along the following path: `./pathname:./.grace/pathname:~/.grace/pathname:$GRACE_HOME/pathname`

### Dynamic modules

Grace can access external functions present in either system or third-party shared libraries or modules specially compiled for use with it. The term dynamic refers to the possibility Grace has to open the library at run time to find the code of the external function, there is no need to recompile Grace itself (the functions already compiled in Grace are "statically linked").

## 3.2 Invocation

### Operational mode

With respect to the user interface, there are three modes of operation that Grace can be invoked in. The full-featured GUI-based version is called `xmgrace`. A batch-printing version is called `gracebat`. A command-line interface mode is called `grace`. Usually, a single executable is called in all cases, with two of the three files being (symbolic) links to a "real" one.

### Command line options

-arrange rows cols

  Arrange the graphs in a grid rows by cols

-autoscale x|y|xy

  Override any parameter file settings

-batch batch_file

  Execute batch_file on start up

-block block_data

  Assume data file is block data

-bxy x:y:etc.

  Form a set from the current block data set using the current set type from columns given in the argument

-cols gcols

  Arrange graphs in gcols columns

-datehint iso|european|us|days|seconds|nohint

  Set the hint for dates analysis

-dpipe descriptor

  Read data from descriptor (anonymous pipe) on startup

-fixed width height

  Set canvas size fixed to width*height

-free

  Use free page layout

-graph graph_number

  Set the current graph number

-graphtype graph_type

  Set the type of the current graph

-hardcopy

  No interactive session, just print and quit

-hdevice hardcopy_device_name

  Set default hardcopy device

-install

  Install private colormap

-legend load

  Turn the graph legend on

-log x|y|xy

  Set the axis scaling of the current graph to logarithmic

-logwindow

  Open the log window

-mono

  Run Grace in monochrome mode (affects the display only)

-noask

  Assume the answer is yes to all requests - if the operation would overwrite a file, Grace will do so without prompting

-noinstall

  Don't use private colormap

-nologwindow

  No log window, overrides resource setting

-noprint

  In batch mode, do not print

-nosigcatch

  Don't catch signals

-npipe file

  Read data from named pipe on startup

-nxy nxy_file

  Assume data file is in X Y1 Y2 Y3 ... format

-param parameter_file

  Load parameters from parameter_file to the current graph

-pexec parameter_string

  Interpret string as a parameter setting

-pipe

  Read data from stdin on startup

-printfile

  file Save print output to file

-remove

  Remove data file after read

-results results_file

  Write the results from regression to results_file

-rows grows

  Arrange graphs in grows rows

-rvideo

  Exchange the color indices for black and white

-saveall save_file

  Save all graphs to save_file

-seed seed_value

  Integer seed for random number generator

-source disk|pipe

  Source type of next data file

-timer delay

  Set allowed time slice for real time inputs to delay ms

-timestamp

  Add timestamp to plot

-settype xy|xydx|...

  Set the type of the next data file

-version

  Show the program version

-viewport xmin ymin xmax ymax

  Set the viewport for the current graph

-wd directory

  Set the working directory

-world xmin ymin xmax ymax

  Set the world coordinates for the current graph

-usage|-help

  This message

## 3.3 Customization

### Environment variables

- GRACE_HOME

  Set the location of Grace. This will be where help files, auxiliary programs, and examples are located. If you are unable to find the location of this directory, contact your system administrator.

- GRACE_PRINT_CMD

  Print command. If the variable is defined but is an empty string, "Print to file" will be selected as default.

- GRACE_EDITOR

  The editor used for manual editing of dataset values.

- GRACE_HELPVIEWER

  The HTML viewer for on-line browsing of help documents

- GRACE_FFTW_WISDOM_FILE and GRACE_FFTW_RAM_WISDOM

  These flags control behavior of the FFTW planner (see README.FFTW for detailed info)

### Init file

Upon start-up, Grace loads its init file, `gracerc`. The file is searched for in the magic path (see magic path); once found, the rest of the path is ignored. It's recommended that in the `gracerc` file, one doesn't use statements which are part of a project file - such defaults, if needed, should be set in the default template (see default template).

### Default template

Whenever a new project is started, Grace loads the default template, `templates/Default.agr`. The file is searched for in the magic path (see magic path); once found, the rest of the path is ignored. It's recommended that in the default template, one doesn't use statements which are NOT part of a project file - such defaults, if needed, should be set in the `gracerc` (see init file).

### X resources

The following Grace-specific X resource settings are supported:

- XMgrace.invertDraw
  Use GXinvert rather than GXxor for rubber-band lines. If the rubber-banding for zooms and lines, etc. doesn't appear on the canvas, set this resource to yes.
- XMgrace.allowDoubleClick
  When Yes, allow double clicks on the canvas to bring up various popups depending on the location of the pointer when the double click occurs.
- XMgrace.toolBar
  Enables button toolbar
- XMgrace.statusBar
  Enables status bar
- XMgrace.locatorBar
  Enables locator bar

It is also possible to customize menus by assigning key accelerators to any item.

You'll need to derive the item's X resource name from the respective menu label, which is easily done following these rules:

- All non-alphanumeric characters are skipped
- Start with lower case; each new word (if any) continues from the capital letter
- Add the item's type to the end - "Menu" for pulldown menus, "Button" for menu buttons.

For example, in order to make Grace popup the Non-linear curve fitting by pressing Control+F, you would add the following two lines

`XMgrace*transformationsMenu.nonLinearCurveFittingButton.acceleratorText: Ctrl+F
XMgrace*transformationsMenu.nonLinearCurveFittingButton.accelerator: Ctrl<Key>f`

to your `.Xresources` file (the file which is read when an X session starts; it could be `.Xdefaults`, `.Xsession` or some other file - ask your system administrator when in doubt).

## 4. Guide to menus and popups

(Not finished yet... Read the Tutorial as well).

## 4.1 File menu

The file menu contains all entries related to the input/output features of Grace.

### New

Reset the state of Grace as if it had just started (one empty graph ranging from 0 to 1 along both axes). If some work has been done and not yet saved, a warning popup is displayed to allow canceling the operation.

### Open

Open an existing project file. A popup is displayed that allow to browse the file system.

### Save

Save the current work in a project file, using the name that was used for the last open or save. If no name has been set (i.e., if the project has been created from scratch) act as save as.

### Save as

Save the current work in a project file with a new name. A popup allows to browse the file system and set the name and the format to use for saving data points (the default value is "%16.8g"). A warning is displayed if a file with the same name already exists.

### Revert to saved

Abandon all modifications performed on the project since the last save. A confirmation popup is fired to allow the user canceling the operation.

### Describe

Open an editable text panel where you can store (or read) a description of the project.

### Read menu

### Sets

Read new sets of data in a graph. A graph selector is used to specify the graph where the data should go (except when reading block data, which are copied to graphs later on).

Reading as "Single set" means that if the source contains only one column of numeric data, one set will be created using the indices (from 1 to the total number of points) as abscissas and read values as ordinates and that if the source contains more than one column of data, the first two numeric columns will be used. Reading as "NXY" means that the first numeric column will provide the abscissas and all remaining columns will provide the ordinates of several sets. Reading as "Block data" means all column will be read and stored and that another popup will allow to select the abscissas and ordinates at will. It should be noted that block data are stored as long as you do not override them by a new read. You can still retrieve data from a block long after having closed all popups, using the set selector.

The set type can be any of:

- XY
- XYDX
- XYDY
- XYDXDX
- XYDYDY
- XYDXDY
- XYDXDXDYDY
- BAR
- BARDY
- BARDYDY
- XYHILO
- XYZ
- XYR

The data source can be selected as "Disk" or "Pipe". In the first case the text in the "Selection" field is considered to be a file name (it can be automatically set by the file selector at the top of the popup). In the latter case the text is considered to be a command which is executed and should produce the data on its standard output. On systems that allows is, the command can be a complete sequence of programs glued together with pipes.

If the source contains date fields, they should be automatically detected. Several formats are recognized (see appendix dates in grace). Calendar dates are converted to numerical dates upon reading.

### NetCDF

This entry exists only if Grace has been installed with support for the NetCDF data format (see configuration).

### Parameters

Retrieve settings previously saved.

### Write menu

### Sets

Save data sets in a file. A set selector is used to specify the set to be saved. The format to use for saving data points can be specified (the default value is "%16.8g"). A warning is displayed if a file with the same name already exists.

### Parameters

Save the parameters either for only the current graph or for all graphs.

### Print

Print the project using the current printer settings

### Device setup

Set the properties of the printing device. Each device has its own set of specific options (see Device-specific settings). According to the device, the output can be sent either directly to a printer or directed to a file. The global settings available for all devices are the sizing parameters.

### Exit

Exit from Grace. If some work has been done and not saved, a warning popup will be displayed to allow the user to cancel the operation.

## 4.2 Edit menu

### Data sets

Using the data set popup, you can view the properties of datasets. This include its type, length, associated comment and main some statistics (min, max, mean, standard deviation). A horizontal scrollbar at the bottom allows to get the two last properties, they are not displayed by default. Also note that if you find some columns are too narrow to show all significant digits, you can drag the vertical rules using Shift+Button 2.

### Set operations

The set operations popup allows you to interact with sets as a whole. If you want to operate on the data ordering of the sets, you should use the data set operations popup from the Data menu. The popup allows you to select a source (one set within one graph) and a destination and perform some action upon them (copy, move, swap). This popup also give you a quick access to several graph and set selectors if you want to perform some other operation like hiding a graph or creating a new set from block data.

### Arrange graphs

This entry fires up a popup to lay out several graphs in a regular grid given rows and columns. The graphs can be packed together (either horizontally or vertically). New graphs are created if needed. An important note is that reducing the number of graphs never delete any graphs! If you select a 6 by 3 grid and then reduce it to 5 by 3, you will still have 18 graphs on your screen, three of them looking strange in the middle of the other ones. This is a security feature that prevent you from losing data accepting too quickly a wrong setting. If you really want to get rid of some of the graphs, you should hide or kill them using any graph selector you can find around (for example in the set operations presented above).

If you don't want the regular layout this arrangement gives you, you can change it afterwards using the mouse (select a graph and double click on the focus marker, see clicks and double clicks).

### Overlay graphs

You can overlay a graph on top of another one. The main use of this feature is to plot several curves using different scales on the same (apparently) graph. The main difficulty is to be sure you operate on the graph you want at all times (you can hide one for a moment if this becomes too difficult).

### Autoscale

Using this entry, you can autoscale one graph or all graphs according to the specified sets only. This is useful if you need either to have truly comparable graphs despite every one contains data of different ranges, or if you want to focus your attention on one set only while it is displayed with other data in a complex graph.

### Regions menu

### Status

This small popup only displays the current state (type and whether it is active or not) of the existing regions.

### Define

You can define a new region (or redefine an existing one), the allowed region types are:

- Inside polygon
- Outside polygon
- Above line
- Below line
- Left of line
- Right of line
- In horizontal range
- In vertical range
- Out of horizontal range
- Out of vertical range

A region can be either linked to the current graph only or to all graphs.

### Clear

This kills a region.

### Report on

This popup reports you which sets or points are inside or outside of a region.

### Hot links

You can link a set to a file or a pipe using this feature. Once a link has been established, you can update it (i.e., read data again) by clicking on the update button. If you have specified a command (using grace language) in the corresponding text field of the popup, it will be executed after each update. Note that you can use several commands separated by ';' characters.

Currently, only simple XY sets can be used for hotlinks.

### Set locator fixed point

After having selected this menu entry, you can select a point on a graph that will be used as the origin of the locator display (just below the menu bar). The fixed point is taken into account only when the display type of the locator is set to [DX,DY].

### Clear locator fixed point

This entry is provided to remove a fixed point set before and use the default again: point [0, 0].

### Locator props

The locator props popup allows you to customize the display of the locator, mainly its type and the format and precision of the display. You can use all the formats that are allowed in the graphs scales.

### Preferences

The preferences popup allows you to set miscellaneous properties of your grace session, such as GUI behavior, cursor type, date reading hint and reference date used for calendar conversions.

## 4.3 Data menu

### Data set operations

This popup gathers all operations that are related to the ordering of data points inside a set or between sets. If you want to operate on the sets as a whole, you should use the set operations popup from the Edit menu. You can sort according to any coordinate (X, Y, DX, ...) in ascending or descending order, reverse the order of the points, join several sets into one, split one set into several others of equal lengths, or drop a range of points from a set. The set selector of the popup shows the number of points in each set in square brackets like this: G0.S0[63], the points are numbered from 0 to n-1.

### Transformations menu

The transformations sub-menu gives you access to all data-mining features of Grace.

### Evaluate expression

Using evaluate expression allows you to create a set by applying an explicit formula to another set, or to parts of another set if you use regions restrictions.

All the classical mathematical functions are available (cos, sin, but also lgamma, j1, erf, ...). As usual all trigonometric functions use radians by default but you can specify a unit if you prefer to say cos (x rad) or sin (3 * y deg). Other predefined names include pi (for the constant) and a, b, c and d for scratch arrays you can use to store data between evaluations.

In the formula, you can use X, Y, Y1, ..., Y4 to denote any coordinate you like from the source set. An implicit loop will be used around your formula so if you say:

> `

>              x = x - 4966.5

> `

you will shift all points of your set 4966.5 units to the left.

You can use more than one set in the same formula, like this:

> `

>              y = y - 0.653 * sin (x deg) + s2.y

> `

which means you use both X and Y from the source set but also the Y coordinate of set 2. Beware that the loop is a simple loop over the indices, all the sets you use in such an hybrid expression should therefore have the same number of points and point i of one set should really be related to point i of the other set. If your sets do not follow these requirements, you should first homogenize them using interpolation.

### Histograms

The histograms popup allows you to compute either standard or cumulative histograms from the Y coordinates of your data. You can select only a range using the start and end fields and you can specify the bin width.

### Fourier transforms

This popup is devoted to direct and inverse Fourier transforms. The default is to perform a direct transform on unfiltered data and to produce a set with the index as abscissa and magnitude as ordinate. You can filter the input data window through triangular, Hanning, Welch, Hamming, Blackman and Parzen filters. You can load magnitude, phase or coefficients and use either index, frequency or period as abscissas. You can choose between direct and inverse Fourier transforms. If you specify real input data, X is assumed to be equally spaced and ignored; if you specify complex input data X is taken as the real part and Y as the imaginary part.

If Grace was configured with the FFTW library (see configuration), then the DFT and FFT buttons really perform the same transform (so there is no speed-up in using FFT in this case). If you want Grace can to use FFTW wisdom files, you should set several environment variables to name them.

### Running averages

The running average popup allows you to compute some values on a sliding window over your data. You choose both the value you need (average, median, minimum, maximum, standard deviation) and the length of the window and perform the operation. You can restrict the operation to the points belonging to (or outside of) a region.

### Differences

The differences popup is used to compute approximations of the first derivative of a function with finite differences. The only choice (apart from the source set of course) is the type of differences to use: forward, backward or centered.

### Seasonal differences

The seasonal differences popup is used to subtract data from a period to data of the preceding period (namely y[i] - y[i + period]). Beware that the period is entered in terms of index in the set and not in terms of abscissa!

### Integration

The integration popup is used to compute the integral of a set and optionally to load it. The numerical value of the integral is shown in the text field after computation. Selecting "cumulative sum" in the choice item will create and load a new set with the integral and compute the end value, selecting "sum only" will only compute the end value.

### Interpolation

The interpolation popup is used to force the abscissas of one set to correspond exactly to the abscissas of another set. This is mainly used before performing some complex operations between the two sets with the evaluate expression popup. Several interpolation methods can be used: linear, spline or Akima splines. Note that if the interpolated set is not wider than the reference set, some extremal points will be missing. You can check this with the number of points of each set (it appears in the set selectors of the popup). In this case you can perform a second run interpolating the reference set at the abscissas of the newly created set, this will remove the extra points.

### Splines

Using the splines popup you can fit a part of a set with cubic or Akima splines. You select which part you want to operate on with the start and stop fields, they are both expressed in abscissa units. The number of points refer to the spline you want to create.

### Regression

The regression popup can be used to fit a set against polynomials or some specific functions (y=A*x^B, y=A*exp(B*x), y=A+B*ln(x) and y=1/(A+Bx)) for which a simple transformation of input data can be used to apply linear regression formulas.

You can load either the fitted values, the residuals or the function itself. Choosing to load fitted values or residuals leads to a set of the same length and abscissas as the initial set. Choosing to load the function is almost similar to load the fitted values except that you choose yourself the boundaries and the number of points. This can be used for example to draw the curve outside of the data sample range or to produce an evenly spaced set from an irregular one.

### Non linear fit

The non linear fit popup can be used for functions outside of the simple regression methods scope. With this popup you provide the expression yourself using a0, a1, ..., an to denote the unknowns (as an example you can say y = a0 * cos (a1 * x + a2)). You specify a tolerance, starting values and optional bounds and run several steps before loading the results.

The fit characteristics (number of parameters, formula, ...) can be saved in a file and retrieved as needed using the file menu of the popup.

You can load either the fitted values, the residuals or the function itself (the choice is in the option menu of the popup). Choosing to load fitted values or residuals leads to a set of the same length and abscissas as the initial set. Choosing to load the function is almost similar to load the fitted values except that you choose yourself the boundaries and the number of points. This can be used for example to draw the curve outside of the data sample range or to produce an evenly spaced set from an irregular one.

### Cross/auto correlation

The correlation popup can be used to compute autocorrelation of one set or cross correlation between two sets. You only select the set (or sets) and specify the maximum lag.

### Digital filter

You can use a set as a weight to filter another set. Only the Y part and the length of the weighting set are important, the X part is ignored.

### Linear convolution

The convolution popup is used to ... convolve two sets. You only select the sets and apply.

### Geometric transforms

You can rotate, scale or translate sets using the geometric transformations popup. You specify the characteristics of each transform and the application order.

### Sample points

This popups provides two sampling methods. The first one is to choose a starting point and a step, the second one is to select only the points that satisfy a boolean expression you specify.

### Prune data

This popup is devoted to reducing huge sets (and then saving both computation time and disk space).

The interpolation method can be applied only to ordered sets: it is based on the assumption that if a real point and an interpolation based on neighboring points are closer than a specified threshold, then the point is redundant and can be eliminated.

The geometric methods (circle, ellipse, rectangle) can be applied to any set, they test each point in turn and keep only those that are not in the neighborhood of previous points.

### Feature extraction

Given a set of curves in a graph, extract a feature from each curve and use the values of the feature to provide the Y values for a new curve.

Feature | Description
Y minimum | Minimum Y value of set
Y maximum | Maximum Y value of set
Y average | Average Y value of set
Y std. dev. | Standard deviation of Y values
Y median | Median Y value
X minimum | Minimum X value of set
X maximum | Maximum X value of set
X average | Average X value of set
X std. dev. | Standard deviation of X values
X median | Median X value
Frequency | Perform DFT (FFT if set length a power of 2) to find largest frequency component
Period | Inverse of above
Zero crossing | Time of the first zero crossing, + or - going
Rise time | Assume curve starts at the minimum and rises to the maximum, get time to go from 10% to 90% of rise. For single exponential curves, this is 2.2*time constant
Fall time | Assume curve starts at the maximum and drops to the minimum, get time to go from 90% to 10% of fall
Slope | Perform linear regression to obtain slope
Y intercept | Perform linear regression to obtain Y-intercept
Set length | Number of data points in set
Half maximal width | Assume curve starts from the minimum, rises to the maximum and drops to the minimum again. Determine the time for which the curve is elevated more than 50% of the maximum rise.
Barycenter X | Barycenter along X axis
Barycenter Y | Barycenter along Y axis
X (Y max) | X of Maximum Y
Y (X max) | Y of Maximum X
integral | cumulative sum
Extractable features

## 4.4 Plot menu

### Plot appearance

The plot appearance popup let you set the time stamp properties and the background color of the page. The color is used outside of graphs and also on graphs were no specific background color is set. The time stamp is updated every time the project is modified.

### Graph appearance

The graph appearance popup can be displayed from both the plot menu and by double-clicking on a legend, title, or subtitle of a graph (see Clicks and double clicks). The graph selector at the top allows to choose the graph you want to operate on, it also allows certain common actions through its popup menu (see graph selector). The main tab includes the properties you will need more often (title for example), and other tabs are used to fine tune some less frequently used options (fonts, sizes, colors, placements).

If you need special characters or special formatting in your title or subtitle, you can use grace escape sequences (the sequence will appear verbatim in the text field but will be rendered on the graph), see typesetting. If you don't remember the mapping between alphabetic characters and the glyph you need in some specific fonts (mainly symbol and zapfdingbats), you can invoke the font tool from the text field by hitting CTRL-e. You can change fonts and select characters from there, they will be copied back in the text field when you press the "Accept" button. Beware of the position of the cursor as you enter text or change font in the font tool, the character or command will be inserted at this position, not at the end of the string!

### Set appearance

The set appearance popup can be displayed from both the plot menu and by double-clicking anywhere in a graph (see Clicks and double clicks). The set selector at the top allows to choose the set you want to operate on, it also allows certain common actions through its popup menu (see set selector). The main tab gathers the properties you will need more often (line and symbol properties or legend string for example), and other tabs are used to fine tune some less frequently used options (drop lines, fill properties, annotated values and error bars properties for example).

You should note that despite the legend string related to one set is entered in the set appearance popup, this is not sufficient to display it. Displaying all legends is a graph level decision, so the toggle is in the main tab of the graph appearance popup.

If you need special characters or special formatting in your legend, you can use grace escape sequences (the sequence will appear verbatim in the text field but will be rendered on the graph), see typesetting. If you don't remember the mapping between alphabetic characters and the glyph you need in some specific fonts (mainly symbol and zapfdingbats), you can invoke the font tool from the text field by hitting CTRL-e. You can change fonts and select characters from there, they will be copied back in the text field when you press the "Accept" button. Beware of the position of the cursor as you enter text or change font in the font tool, the character or command will be inserted at this position, not at the end of the string!

### Axis properties

The axis properties popup can be displayed from both the "Plot" menu and by double-clicking exactly on an axis (see Clicks and double clicks). The pulldown menu at the top allows to select the axis you want to operate on. The "Active" toggle globally activates or deactivates the axis (all GUI elements are insensitive for deactivated axes). The start and stop fields depict the displayed range. Three types of scales are available: linear, logarithmic or reciprocal, and you can invert the axis (which normally increases from left to right and from bottom to top). The main tab includes the properties you will need more often (axis label, tick spacing and format for example), and other tabs are used to fine tune some less frequently used options (fonts, sizes, colors, placements, stagger, grid lines, special ticks, ...).

If you need special characters or special formatting in your label, you can use grace escape sequences (the sequence will appear verbatim in the text field but will be rendered on the graph), see typesetting. If you don't remember the mapping between alphabetic characters and the glyph you need in some specific fonts (mainly symbol and zapfdingbats), you can invoke the font tool from the text field by hitting CTRL-e. You can change fonts and select characters from there, they will be copied back in the text field when you press the "Accept" button. Beware of the position of the cursor as you enter text or change font in the font tool, the character or command will be inserted at this position, not at the end of the string!

Once you have set the options as you want, you can apply them. One useful feature is that you can set several axes at once with the bottom pulldown menu (current axis, all axes current graph, current axis all graphs, all axes all graphs). Beware that you always apply the properties of all tabs, not only the selected one.

## 4.5 View menu

### Show locator bar

This toggle item shows or hides the locator below the menu bar.

### Show status bar

This toggle item shows or hides the status string below the canvas.

### Show tool bar

This toggle item shows or hides the tool bar at the left of the canvas.

### Redraw

This menu item triggers a redrawing of the canvas.

### Update all

This menu item causes an update of all GUI controls. Usually, everything is updated automatically, unless one makes modifications by entering commands in the Command tool.

## 4.6 Window menu

### Commands

### Point tracking

### Drawing objects

### Font tool

### Results

## 4.7 Help menu

### On context

This function is not implemented yet.

### User's guide

Browse the Grace user's guide.

### Tutorial

Browse the Grace tutorial.

### FAQ

Frequently Asked Questions with answers.

### Changes

The list of changes during the Grace development.

### Examples

The whole tree of submenus each loading a sample plot.

### Comments

Use this to send your suggestions or bug reports.

### License terms

Grace licensing terms will be displayed (GPL version 2).

### About

A popup with basic info on the software, including some configuration details. More details can be found when running Grace with the "-version" command line flag.

## 5. GUI controls

## 5.1 List selectors

Various selectors are available in several popups. They all display lists of objects (graphs, sets, ...) and can be used to perform simple operations on these objects (copying, deleting, ...). The operations are available from a popup menu that appears when pressing mouse button 3 on them. Depending on the required functionality, they may allow multiple choices or not. The following shortcuts are enabled (if the result of an action would contradict the list's selection policy, this would be ignored):

- Ctrl+a select all
- Ctrl+u unselect all
- Ctrl+i invert selection

### Graph selector

The operations that can be performed on graphs through the graph selector's menu popup are:

- focus to
- hide
- show
- duplicate
- kill
- swap
- create new

All this operations are not available in every instance of the selector. For example in the "read sets" popup only one graph can be selected at a time, and the swap operation is disabled.

Double-clicking on a list entry will switch the focus to that graph.

### Set selector

The operations that can be performed on sets through the set selector are:

- hide
- show
- bring to front
- send to back
- duplicate
- kill
- kill data
- swap
- edit
  - in spreadsheet
  - in text editor
- create new
  - by formula
  - in spreadsheet
  - in text editor
  - from block data
- pack all sets
- selectors operations
  - show data-less
  - show hidden
  - select all
  - unselect all
  - invert selection
  - update

## 6. Canvas actions

## 6.1 Hotkeys

When the pointer focus is on the canvas (where the graph is drawn), there are some shortcuts to activate several actions. They are:

- Ctrl <Key>A: Autoscale
- Ctrl <Key>D: Delete an object
- Ctrl <Key>L: Move current graph legend
- Ctrl <Key>M: Move an object
- Ctrl <Key>T: Place timestamp
- Ctrl <Key>U: Refresh hotlinks
- Ctrl <Key>V: Set the viewport with mouse
- Ctrl <Key>Z: Zoom
- Ctrl Alt <Key>L: Draw a line
- Ctrl Alt <Key>B: Draw a box
- Ctrl Alt <Key>E: Draw an ellipse
- Ctrl Alt <Key>T: Write a text string

## 6.2 Clicks and double clicks

A single click inside a graph switches focus to that graph. This is the default policy, but it can be changed from the "Edit/Preferences" popup.

Double clicking on parts of the canvas will invoke certain actions or raise some popups:

- on a focus marker: move selected viewport corner
- on an axis: "Axis properties" popup
- on a set: "Set appearance" popup
- on a legend: "Graph appearance" popup
- on a (sub)title: "Graph appearance" popup
- on an object (box, line, ...): a popup for editing properties of that object

The double clicking actions can be enabled/disabled from the "Edit/Preferences" popup.

## 7. Command interpreter

## 7.1 Definitions

Not written yet...

## 7.2 Graph properties

Not written yet...

## 7.3 Set properties

Not written yet...

## 7.4 Device parameters

Command | Description
PAGE SIZE xdim, ydim | set page dimensions (in pp) of all devices
DEVICE "devname" PAGE SIZE xdim, ydim | set page dimensions (in pp) of device devname
DEVICE "devname" DPI dpi | set device's dpi (dots per pixel)
DEVICE "devname" FONT onoff | enable/disable usage of built-in fonts for device devname
DEVICE "devname" FONT ANTIALIASING onoff | enable/disable font aliasing for device devname
DEVICE "devname" OP "options" | set device specific options (see Device-specific settings)
HARDCOPY DEVICE "devname" | set device devname as current hardcopy device
Device parameters.

## 7.5 Functions and variables

Not written yet...

## 7.6 Procedures

Not written yet...

## 8. Advanced topics

## 8.1 Adding/replacing fonts

## 8.2 Interaction with other applications

### Using pipes

### Using grace_np library

The grace_np library is a set of compiled functions that allows you to launch and drive a Grace subprocess from your C or Fortran application. Functions are provided to start the subprocess, to send it commands or data, to stop it or detach from it.

Function | Arguments | Description
int GraceOpen | (int buf_size) | launch a Grace subprocess and open a communication channel with it
int GraceIsOpen | (void) | test if a Grace subprocess is currently connected
int GraceClose | (void) | close the communication channel and exit the Grace subprocess
int GraceClosePipe | (void) | close the communication channel and leave the Grace subprocess alone
int GraceFlush | (void) | flush all the data remaining in the buffer
int GracePrintf | (const char* format, ...) | format a command and send it to the Grace subprocess
int GraceCommand | (const char* cmd) | send an already formated command to the Grace subprocess
GraceErrorFunctionType GraceRegisterErrorFunction | (GraceErrorFunctionType f) | register a user function f to display library errors
grace_np library C functions.

Function | Arguments | Description
integer GraceOpenF | (integer buf_size) | launch a Grace subprocess and open a communication channel with it
integer GraceIsOpenF | (void) | test if a Grace subprocess is currently connected
integer GraceCloseF | (void) | close the communication channel and exit the Grace subprocess
integer GraceClosePipeF | (void) | close the communication channel and leave the Grace subprocess alone
integer GraceFlushF | (void) | flush all the data remaining in the buffer
integer GraceCommandF | (character*(*) cmd) | send an already formatted command to the Grace subprocess
GraceFortranFunctionType GraceRegisterErrorFunctionF | (GraceFortranFunctionType f) | register a user function f to display library errors
grace_np library F77 functions.

There is no fortran equivalent for the GracePrintf function, you should format all the data and commands yourself before sending them with GraceCommandF.

The Grace subprocess listen for the commands you send and interpret them as if they were given in a batch file. You can send any command you like (redraw, autoscale, ...). If you want to send data, you should include them in a command like "g0.s0 point 3.5, 4.2".

Apart from the fact it monitors the data sent via an anonymous pipe, the Grace subprocess is a normal process. You can interact with it through the GUI. Note that no error can be sent back to the parent process. If your application send erroneous commands, an error popup will be displayed by the subprocess.

If you exit the subprocess while the parent process is still using it, the broken pipe will be detected. An error code will be returned to every further call to the library (but you can still start a new process if you want to manage this situation).

Here is an example use of the library, you will find this program in the distribution.

> `

>     #include <stdlib.h>
>     #include <stdio.h>
>     #include <unistd.h>
>     #include "grace_np.h"

>     #ifndef EXIT_SUCCESS
>     #  define EXIT_SUCCESS 0
>     #endif

>     #ifndef EXIT_FAILURE
>     #  define EXIT_FAILURE -1
>     #endif

>     void my_error_function(const char *msg)
>     {
>         fprintf(stderr, "library message: \"%s\"\n", msg);
>     }

>     int
>     main(int argc, char* argv[])
>     {
>         int i;

>         GraceRegisterErrorFunction(my_error_function);

>         /* Start Grace with a buffer size of 2048 and open the pipe */
>         if (GraceOpen(2048) == -1) {
>             fprintf(stderr, "Can't run Grace. \n");
>             exit(EXIT_FAILURE);
>         }

>         /* Send some initialization commands to Grace */
>         GracePrintf("world xmax 100");
>         GracePrintf("world ymax 10000");
>         GracePrintf("xaxis tick major 20");
>         GracePrintf("xaxis tick minor 10");
>         GracePrintf("yaxis tick major 2000");
>         GracePrintf("yaxis tick minor 1000");
>         GracePrintf("s0 on");
>         GracePrintf("s0 symbol 1");
>         GracePrintf("s0 symbol size 0.3");
>         GracePrintf("s0 symbol fill pattern 1");
>         GracePrintf("s1 on");
>         GracePrintf("s1 symbol 1");
>         GracePrintf("s1 symbol size 0.3");
>         GracePrintf("s1 symbol fill pattern 1");

>         /* Display sample data */
>         for (i = 1; i <= 100 && GraceIsOpen(); i++) {
>             GracePrintf("g0.s0 point %d, %d", i, i);
>             GracePrintf("g0.s1 point %d, %d", i, i * i);
>             /* Update the Grace display after every ten steps */
>             if (i % 10 == 0) {
>                 GracePrintf("redraw");
>                 /* Wait a second, just to simulate some time needed for
>                    calculations. Your real application shouldn't wait. */
>                 sleep(1);
>             }
>         }

>         if (GraceIsOpen()) {
>             /* Tell Grace to save the data */
>             GracePrintf("saveall \"sample.agr\"");

>             /* Flush the output buffer and close Grace */
>             GraceClose();

>             /* We are done */
>             exit(EXIT_SUCCESS);
>         } else {
>             exit(EXIT_FAILURE);
>         }
>     }

> `

## 8.3 FFTW tuning

When the FFTW capabilities are compiled in, Grace looks at two environment variables to decide what to do with the FFTW 'wisdom' capabilities. First, a quick summary of what this is. The FFTW package is capable of adaptively determining the most efficient factorization of a set to give the fastest computation. It can store these factorizations as 'wisdom', so that if a transform of a given size is to be repeated, it is does not have to re-adapt. The good news is that this seems to work very well. The bad news is that, the first time a transform of a given size is computed, if it is not a sub-multiple of one already known, it takes a LONG time (seconds to minutes).

The first environment variable is GRACE_FFTW_WISDOM_FILE. If this is set to the name of a file which can be read and written (e.g., $HOME/.grace_fftw_wisdom) then Grace will automatically create this file (if needed) and maintain it. If the file is read-only, it will be read, but not updated with new wisdom. If the symbol GRACE_FFTW_WISDOM_FILE either doesn't exist, or evaluates to an empty string, Grace will drop the use of wisdom, and will use the fftw estimator (FFTW_ESTIMATE flag sent to the planner) to guess a good factorization, instead of adaptively determining it.

The second variable is GRACE_FFTW_RAM_WISDOM. If this variable is defined to be non-zero, and GRACE_FFTW_WISDOM_FILE variable is not defined (or is an empty string), Grace will use wisdom internally, but maintain no persistent cache of it. This will result in very slow execution times the first time a transform is executed after Grace is started, but very fast repeats. I am not sure why anyone would want to use wisdom without writing it to disk, but if you do, you can use this flag to enable it.

## 8.4 DL modules

Since version 4.1.1, Grace can access external functions present in either system or third-party shared libraries or modules specially compiled for use with Grace.

### Function types

One must make sure, however, that the external function is of one of supported by Grace types:

Grace type | Description
f_of_i | a function of 1 `int` variable
f_of_d | a function of 1 `double` variable
f_of_nn | a function of 2 `int` parameters
f_of_nd | a function of 1 `int` parameter and 1 `double` variable
f_of_dd | a function of 2 `double` variables
f_of_nnd | a function of 2 `int` parameters and 1 `double` variable
f_of_ppd | a function of 2 `double` parameters and 1 `double` variable
f_of_pppd | a function of 3 `double` parameters and 1 `double` variable
Grace types for external functions

The return values of functions are assumed to be of the `double` type.

Note, that there is no difference from the point of view of function prototype between parameters and variables; the difference is in the way Grace treats them - an attempt to use a vector expression as a parameter argument will result in a parse error.

Let us consider few examples.

### Examples

Caution: the examples provided below (paths and compiler flags) are valid for Linux/ELF with gcc. On other operating systems, you may need to refer to compiler/linker manuals or ask a guru.

### Example 1

Suppose I want to use function `pow(x,y)` from the Un*x math library (libm). Of course, you can use the "^" operator defined in the Grace language, but here, for the sake of example, we want to access the function directly.

The command to make it accessible by Grace is

> `USE "pow" TYPE f_of_dd FROM "/usr/lib/libm.so"`

Try to plot y = pow(x,2) and y = x^2 graphs (using, for example, "create new -> Formula" from any set selector) and compare.

### Example 2

Now, let us try to write a function ourselves. We will define function `my_function` which simply returns its (second) argument multiplied by integer parameter transferred as the first argument.

In a text editor, type in the following C code and save it as "my_func.c":

> `

>            double my_function (int n, double x)
>            {
>                double retval;
>                retval = (double) n * x;
>                return (retval);
>            }

> `

OK, now compile it:

> `

>            $gcc -c -fPIC my_func.c
>            $gcc -shared my_func.o -o /tmp/my_func.so

> `

(You may strip it to save some disk space):

> `

>            $strip /tmp/my_func.so

> `

That's all! Ready to make it visible to Grace as "myf" - we are too lazy to type the very long string "my_function" many times.

> `USE "my_function" TYPE f_of_nd FROM "/tmp/my_func.so" ALIAS "myf"`

### Example 3

A more serious example. There is a special third-party library available on your system which includes a very important for you yet very difficult-to-program from the scratch function that you want to use with Grace. But, the function prototype is NOT one of any predefined types. The solution is to write a simple function wrapper. Here is how:

Suppose, the name of the library is "special_lib" and the function you are interested in is called "special_func" and according to the library manual, should be accessed as `void special_func(double *input, double *output, int parameter)`. The wrapper would look like this:

> `

>            double my_wrapper(int n, double x)
>            {
>                extern void special_func(double *x, double *y, int n);
>                double retval;
>                (void) special_func(&x, &retval, n);
>                return (retval);
>            }

> `

Compile it:

> `

>            $gcc -c -fPIC my_wrap.c
>            $gcc -shared my_wrap.o -o /tmp/my_wrap.so -lspecial_lib -lblas
>            $strip /tmp/my_wrap.so

> `

Note that I added `-lblas` assuming that the special_lib library uses some functions from the BLAS. Generally, you have to add all libraries which your module depends on (and all libraries those libraries rely upon etc.), as if you wanted to compile a plain executable.

Fine, make Grace aware of the new function

> `USE "my_wrapper" TYPE f_of_nd FROM "/tmp/my_wrap.so" ALIAS "special_func"`

so we can use it with its original name.

### Example 4

An example of using Fortran modules.

Here we will try to achieve the same functionality as in Example 2, but with the help of F77.

> `

>            DOUBLE PRECISION FUNCTION MYFUNC (N, X)
>            IMPLICIT NONE
>            INTEGER N
>            DOUBLE PRECISION X
>     C
>            MYFUNC = N * X
>     C
>            RETURN
>            END

> `

As opposite to C, there is no way to call such a function from Grace directly - the problem is that in Fortran all arguments to a function (or subroutine) are passed by reference. So, we need a wrapper:

> `

>            double myfunc_wrapper(int n, double x)
>            {
>                extern double myfunc_(int *, double *);
>                double retval;
>                retval = myfunc_(&n, &x);
>                return (retval);
>            }

> `

Note that most of f77 compilers by default add underscore to the function names and convert all names to the lower case, hence I refer to the Fortran function `MYFUNC` from my C wrapper as `myfunc_`, but in your case it can be different!

Let us compile the whole stuff:

> `

>            $g77 -c -fPIC myfunc.f
>            $gcc -c -fPIC myfunc_wrap.c
>            $gcc -shared myfunc.o myfunc_wrap.o -o /tmp/myfunc.so -lf2c -lm
>            $strip /tmp/myfunc.so

> `

And finally, inform Grace about this new function:

> `USE "myfunc_wrapper" TYPE f_of_nd FROM "/tmp/myfunc.so" ALIAS "myfunc"`

## 9. References

## 9.1 Typesetting

Grace permits quite complex typesetting on a per string basis. Any string displayed (titles, legends, tick marks,...) may contain special control codes to display subscripts, change fonts within the string etc.

Control code | Description
\f{x} | switch to font named "x"
\f{n} | switch to font number n (not recommended)
\f{} | return to original font
\u | begin underline
\U | stop underline
\o | begin overline
\O | stop overline
\c | begin using upper 128 characters of set
\C | stop using upper 128 characters of set
\z{x} | zoom x times
\z{} | return to original zoom
\v{x} | shift vertically by x
\v{} | return to unshifted baseline
\h{x} | horizontal shift by x
\m{n} | mark current position as n
\M{n} | return to saved position n
\dl | LtoR substring direction
\dr | RtoL substring direction
\dL | LtoR text advancing
\dR | RtoL text advancing
\x | switch to Symbol font (same as \f{Symbol})
\+ | increase size (same as \z{1.19} ; 1.19 = sqrt(sqrt(2)))
\- | decrease size (same as \z{0.84} ; 0.84 = 1/sqrt(sqrt(2)))
\s | begin subscripting (same as \v{-0.4}\z{0.71})
\S | begin superscripting (same as \v{0.6}\z{0.71})
\N | return to normal style (same as \v{}\z{})
\\ | print \
Control codes.

Example:

F\sX\N(\xe\f{}) = sin(\xe\B)\c7\Ce\S-X\N\c7\Ccos(\xe\f{})

prints roughly

> `

>                            -x
>            F (e) = sin(e)·e  ·cos(e)
>             x

> `

using string's initial font and e prints as epsilon from the Symbol font.

NOTE: Characters from the upper half of the char table can be entered directly from the keyboard, using appropriate `xmodmap(1)` settings, or with the help of the font tool ("Window/Font tool").

## 9.2 Device-specific limitations

Grace can output plots using several device backends. The list of available devices can be seen (among other stuff) by specifying the "-version" command line switch.

- X11, PostScript and EPS are full-featured devices
- Raster drivers (PNM/JPEG/PNG):
  - only even-odd fill rule is supported
  - patterned lines are not implemented
- PDF driver:
  - patterned fills are not implemented
  - bitmapped text strings are not transparent
  - arcs of angles != 90*n are approximated very roughly

## 9.3 Device-specific settings

Some of the output devices accept several configuration options. You can set the options by passing a respective string to the interpreter using the "DEVICE "devname" OP "options"" command (see Device parameters). A few options can be passed in one command, separated by commas.

Command | Description
grayscale | set grayscale output
color | set color output
level1 | use only PS Level 1 subset of commands
level2 | use also PS Level 2 commands if needed
xoffset:x | set page offset in X direction x pp
yoffset:y | set page offset in Y direction y pp
PostScript driver options

Command | Description
grayscale | set grayscale output
color | set color output
bbox:tight | enable "tight" bounding box
bbox:page | bounding box coincides with page dimensions
EPS driver options

Command | Description
format:pbm | output in PBM format
format:pgm | output in PGM format
format:ppm | output in PPM format
rawbits:on | "rawbits" (binary) output
rawbits:off | ASCII output
PNM driver options

Command | Description
grayscale | set grayscale output
color | set color output
optimize:on/off | enable/disable optimization
quality:value | set compression quality (0 - 100)
smoothing:value | set smoothing (0 - 100)
baseline:on/off | do/don't force baseline output
progressive:on/off | do/don't output in progressive format
dct:ifast | use fast integer DCT method
dct:islow | use slow integer DCT method
dct:float | use floating-point DCT method
JPEG driver options

Command | Description
interlaced:on | make interlaced image
interlaced:off | don't make interlaced image
transparent:on | produce transparent image
transparent:off | don't produce transparent image
compression:value | set compression level (0 - 9)
PNG driver options

## 9.4 Dates in Grace

We use two calendars in Grace: the one that was established in 532 by Denys and lasted until 1582, and the one that was created by Luigi Lilio (Alyosius Lilius) and Christoph Klau (Christophorus Clavius) for pope Gregorius XIII. Both use the same months (they were introduced under emperor Augustus, a few years after Julian calendar introduction, both Julius and Augustus were honored by a month being named after each one).

The leap years occurred regularly in Denys's calendar: once every four years, there is no year 0 in this calendar (the leap year -1 was just before year 1). This calendar was not compliant with earth motion and the dates were slowly shifting with regard to astronomical events.

This was corrected in 1582 by introducing Gregorian calendar. First a ten days shift was introduced to reset correct dates (Thursday October the 4th was followed by Friday October the 15th). The rules for leap years were also changed: three leap years are removed every four centuries. These years are those that are multiple of 100 but not multiple of 400: 1700, 1800, and 1900 were not leap years, but 1600 and 2000 were (will be) leap years.

We still use Gregorian calendar today, but we now have several time scales for increased accuracy. The International Atomic Time is a linear scale: the best scale to use for scientific reference. The Universal Time Coordinate (often confused with Greenwich Mean Time) is a legal time that is almost synchronized with earth motion. However, since the earth is slightly slowing down, leap seconds are introduced from time to time in UTC (about one second every 18 months). UTC is not a continuous scale ! When a leap second is introduced by International Earth Rotation Service, this is published in advance and the legal time sequence is as follows: 23:59:59 followed one second later by 23:59:60 followed one second later by 00:00:00. At the time of this writing (1999-01-05) the difference between IAT and UTC was 32 seconds, and the last leap second was introduced in 1998-12-31.

These calendars allow to represent any date from the mist of the past to the fog of the future, but they are not convenient for computation. Another time scale is possible: counting only the days from a reference. Such a time scale was introduced by Joseph-Juste Scaliger (Josephus Justus Scaliger) in 1583. He decided to use "-4713-01-01 12:00:00" as a reference date because it was at the same time a Monday, first of January of a leap year, there was an exact number of 19 years Meton cycle between this date and year 1 (for Easter computation), and it was at the beginning of a 15 years Roman indiction cycle. The day number counted from this reference is traditionally called Julian day, but it has really nothing to do with the Julian calendar.

Grace stores dates internally as reals numbers counted from a reference date. The default reference date is the one chosen by Scaliger but can modified either for a single session (using the -dateref command line flag, the Edit->Preferences popup of the GUI). If you often work with a specific reference date you can set it in a REFERENCE DATE command in your configuration file (see Default template).

The following date formats are supported (hour, minutes and seconds are always optional):

1. iso8601 : 1999-12-31 23:59:59.999
2. european : 31/12/1999 23:59:59.999 or 31/12/99 23:59:59.999
3. us : 12/31/1999 23:59:59.999 or 12/31/99 23:59:59.999
4. Julian : 123456.789

You can also provide a hint about the format ("ISO8601", "european", "us") using the -datehint command line flag or the ref name="Edit->Preferences" id="preferences"> popup of the GUI. The formats are tried in the following order: first the hint given by the user, then iso, european and us (there is no ambiguity between calendar formats and numerical formats and therefore no order is specified for them). The separators between various fields can be any characters in the set: " :/.-" (one or more spaces act as one separator, other characters can not be repeated), so the string "1999-12 31:23/59" is allowed (but not recommended). The '-' character is used both as a separator (it is traditionally used in iso8601 format) and as the unary minus (for dates in the far past or for numerical dates). By default years are left untouched, so 99 is a date far away in the past. This behavior can be changed with the Edit->preferences popup, or with the `DATE WRAP on` and `DATE WRAP YEAR year` commands. Suppose for example that the wrap year is chosen as 1950, if the year is between 0 and 99 and is written with two or less digits, it is mapped to the present era as follows:

range [00 ; 49] is mapped to [2000 ; 2049]

range [50 ; 99] is mapped to [1950 ; 1999]

with a wrap year set to 1970, the mapping would have been:

range [00 ; 69] is mapped to [2000 ; 2069]

range [70 ; 99] is mapped to [1970 ; 1999]

this is reasonably Y2K compliant and is consistent with current use. Specifying year 1 is still possible using more than two digits as follows: "0001-03-04" is unambiguously March the 4th, year 1. The inverse transform is applied for dates written by Grace, for example as tick labels. Using two digits only for years is not recommended, we introduce a wrap year + 100 bug here so this feature should be removed at some point in the future ...

Numerical (Julian) dates are computed according to a customizable reference date. The default value is given by the REFERENCE DATE command (you can set it in your configuration files). The default value is "-4713-01-01 12:00:00", it is a classical reference for astronomical events (note that the '-' is used here both as a unary minus and as a separator).

The date scanner can be used either for Denys's and Gregorian calendars. Inexistent dates are detected, they include year 0, dates between 1582-10-05 and 1582-10-14, February 29th of non leap years, months below 1 or above 12, ... the scanner does not take into account leap seconds: you can think it works only in International Atomic Time (IAT) and not in Unified Time Coordinate (UTC). If you find yourself in a situation were you need UTC, a very precise scale, and should take into account leap seconds ... you should convert your data yourself (for example using International Atomic Time). But if you bother with that you probably already know what to do.

## 9.5 Xmgr to Grace migration guide

This is a very brief guide describing problems and workarounds for reading in project files saved with Xmgr. You should read the docs or just play with Grace to test new features and controls.

1. DOCUMENTATION IS VERY SPARSE YET!
2. Grace must be explicitly told the version number of the software used to create a file. You can manually put "@version VERSIONID" string in the beginning of the file. The VERSIONID is built as MAJOR_REV*10000 + MINOR_REV*100 + PATCHLEVEL; so 40101 corresponds to xmgr-4.1.1. Projects saved with Xmgr-4.1.2 do NOT need the above, since they already have the version string in them.
3. The above relates to the ASCII projects only. The old binary projects (saved with xmgr-4.0.*) are not automatically converted anymore. An input filter must be defined to make the conversion work on-the-fly. Add the following line to /.gracerc or the system-wide $GRACE_HOME/gracerc resource file: DEFINE IFILTER "grconvert %s -" MAGIC "00000031" See docs for more info on the I/O filters.
4. Grace is WYSIWYG. Xmgr was not. Many changes required to achieve the WYSIWYG'ness led to the situation when graphs with objects carefully aligned under Xmgr may not look so under Grace. Grace tries its best to compensate for the differences, but sometimes you may have to adjust such graphs manually.
5. Smith plots don't work now. They'll be put back soon.
6. A lot of symbol types (all except *real* symbols) are removed. "Location *" types can be replaced (with much higher comfort) by A(nnotating)values. "Impulse *", "Histogram *" and "Stair steps *" effects can be achieved using the connecting line parameters (Type, Drop lines). "Dot" symbol is removed as well; use the filled circle symbol of the zero size with no outline to get the same effect.
7. Default page layout switched from free (allowing to resize canvas with mouse) to fixed. For the old behavior, put "PAGE LAYOUT FREE" in the Grace resource file or use the "-free" command line switch. The use of the "free" page layout is in general deprecated, though.
8. System variables GR_* renamed to GRACE_*