void contour (fun, x, nx, y, ny, min, step, max, lnstyle, labint) CNTPLT.C Level 3
float (*fun)(float, float) A user-defined function which returns z = fun(x,y).
float *x The x vector.
int nx The number of x values (must be odd).
float *y The y vector.
int ny The number of y values (must be odd).
float min The minimum contour level.
float step The interval between contour levels.
float max The maximum contour level.
int *lnstyle An array of coded numbers for changing line styles and/or colors for each contour level. See the explanation at the beginning of this section. This specification will not handle the extended GraphiC colors and is retained for compatibility purposes. 
If lnstyle == NULL, the more powerful specification capability of contcolor() will be used (recommended).
int labint Labels are placed on every labint contour.
If labint = 0, contour labels are suppressed.
contour() produces level contours for the function fun(x, y). That is, for each value of level C, the curve fun(x, y
= C is plotted. For best results, the size of the x-y grid squares should be small compared to the length in which fun(x, y) varies significantly. contour() creates its own array of linearly spaced levels. Because contour() must evaluate the function on each grid point, it can take a long time to do this, especially if the function is complicated and if you don't have a math coprocessor.