void surfun (zfun, ixpts, xdel, iypts, ydel) D3PLT.C Level 3
 
float (*zfun)(float,float) A function that determines the height of the surface from the x-y plane. 
The arguments of zfun are float x, float y.
int ixpts Number of points interpolated between grid lines in the x direction.
float xdel Interval between grid lines on the x axis in units of the x axis.
int iypts Number of points interpolated between grid lines in the y direction.
float ydel Interval between grid lines on the y axis in units of the y axis.
 
surfun() draws the surface z = zfun(x, y) as a grid of lines parallel to the x and y axes. By increasing the values of ixpts and iypts, the smoothness of the surface will be increased.