void surmat (zmat, xdim, ydim)

void surmat2 (zmat, xdim, ydim)

D3PLT.C Level 3
float *zmat A matrix of values zmat[y][x] that determines the height of the surface from the x-y plane. zmat must be allocated as a single piece of memory in surmat(), and using dim2() in surmat2().
int xdim, ydim The x and y dimensions of the matrix.
surmat() works like surfun() to draw a surface above the x-y plane. In this case, you supply the array of grid values. 
surmat2() will allow the use of much larger memory arrays up to 64 kb per row (in DOS and Windows 3.1), and array access will be faster.