Scilab Function
Last update : 02/09/2005

contour2d - level curves of a surface on a 2D plot

### Calling Sequence

  `contour2d(x,y,z,nz,[style,strf,leg,rect,nax])`
  `contour2d(x,y,z,nz,<opt_args>)`

### Parameters

- `x,y`: two real row vectors of size n1 and n2: the grid.
- `z`: real matrix of size (n1,n2), the values of the function on the grid or a Scilab function which defines the surface `z=f(x,y)`.
- `nz`: the level values or the number of levels.
  - `-`If `nz` is an integer, its value gives the number of level curves equally spaced from zmin to zmax as follows:

        z= zmin + (1:nz)*(zmax-zmin)/(nz+1)

    Note that the `zmin` and `zmax` levels are not drawn (generically they are reduced to points) but they can be added with

        [im,jm] = find(z == zmin); // or zmax
        plot2d(x(im)',y(jm)',-9,"000")

  - `-`If `nz` is a vector, `nz(i)` gives the value of the ith level curve.
- `<opt_args>`: This represents a sequence of statements `key1=value1,key2=value2`,... where `key1`, `key2,...` can be one of the following: style, leg, rect, nax, strf or axesflag and frameflag (see `plot2d`)
- `style,strf,leg,rect,nax`: see `plot2d`. The argument `style` gives the dash styles or colors which are to be used for level curves. It must have the same size as the number of levels.

### Description

`contour2d` draws level curves of a surface `z=f(x,y)` on a 2D plot. The values of `f(x,y)` are given by the matrix `z` at the grid points defined by `x` and `y`.

You can change the format of the floating point number printed on the levels by using `xset("fpf",string)` where `string` gives the format in C format syntax (for example `string="%.3f"`). Use `string=""` to switch back to default format and Use `string=" "` to suppress printing. This last feature is useful in conjunction with `legends` to display the level numbers in a legend and not directly onto the level curves as usual (see Examples).

The optional arguments `style,strf,leg,rect,nax`, can be passed by a sequence of statements `key1=value1, key2=value2`, ... where keys may be `style`,`strf`,`leg`,`rect`,`nax`. In this case, the order has no special meaning.

Use `contour` to draw levels curves on a 3D surface.

### Examples

    contour2d(1:10,1:10,rand(10,10),5,rect=[0,0,11,11])
    // changing the format of the printing of the levels
    xset("fpf","%.2f")
    clf()
    contour2d(1:10,1:10,rand(10,10),5,rect=[0,0,11,11])

    // now an example with level numbers drawn in a legend
    // Caution there are a number of tricks...
    x = linspace(0,4*%pi,80);
    z = cos(x')*cos(x);
    clf(); f=gcf();
    xset("fpf"," ")  // trick 1: this implies that the level numbers are not
                     //          drawn on the level curves
    f.color_map=jetcolormap(7);
    // trick 2: to be able to put the legend on the right without
    //          interfering with the level curves use rect with a xmax
    //          value large enough
    contour2d(x,x,z,-0.75:0.25:0.75,frameflag=3,rect=[0,0,5*%pi,4*%pi])
    // trick 3: use legends (note that the more practical legend function
    //          will not work as soon as one of the level is formed by 2 curves)
    legends(string(-0.75:0.25:0.75),1:7,"lr");
    xtitle("Some level curves of the function cos(x)cos(y)")

### See Also

`contour`, `contour2di`, `plot2d`,

### Author

J.Ph.C.