eval3d - values of a function on a grid
This function returns a matrix z(n1,n2). z(i,j)=fun(x(i),y(j)). If the function fun doesn't accept arguments of type vector use the primitive feval.
x=-5:5;y=x;
deff('[z]=f(x,y)',['z= x.*y']);
z=eval3d(f,x,y);
plot3d(x,y,z);
//
deff('[z]=f(x,y)',['z= x*y']);
z=feval(x,y,f);
plot3d(x,y,z);