contour2di compute level curves of a surface on a 2D plot

## Syntax

    [xc, yc] = contour2di(x, y, z, nz)

## Arguments

x, y

  two real row vectors of size `n1` and `n2`: the grid.

z

  a real matrix of size `(n1,n2)`, the values of the function.

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 `i`-th level curve.

xc, yc

  vectors of identical sizes containing the contours definitions. See below for details.

## Description

`contour2di` computes 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`.

`xc(1)` contains the level associated with first contour path, `yc(1)` contains the number `N1` of points defining this contour path and (`xc(1+(1:N1))`, `yc(1+(1:N1))` ) contain the coordinates of the paths points. The second path begin at `xc(2+N1)` and `yc(2+N1)` and so on.

## Examples

    [xc,yc]=contour2di(1:10,1:10,rand(10,10),5);
    k=1;n=yc(k);c=1;
    while k+yc(k)<size(xc,'*')
      n=yc(k);
      plot2d(xc(k+(1:n)),yc(k+(1:n)),c)
      c=c+1;
      k=k+n+1;
    end

## See also

- contour
- contour2d
- contour2dm
- plot2d