Hello,

if I remember correctly, I came across some code in povray or one of its
patches that calculates the gradient of a pattern or function. By this
I mean a function that numerically finds the direction of a real valued
function f at some point p in space in which f increases most. This was 
done by evaluating the function slightly off p. To improve numerical 
stability, the code in question used the four vertices of a tetrahedron 
and evaluated the function f there. So, if v1,...,v4 denote the vertices
of a tetrahedron centered at the origin, the function f was evaluated at
p+v1, p+v2, p+v3 and p+v4.

Unfortunately I cannot find this code anymore. Does somebody know what
I'm writing about and the file to look at?

Thanks in advance.
Thomas

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