# Ask for help with Divergence in Derive 6

1. Aug 7, 2011

### pogono

Hello,
I have a problem with divergence function DIV in DERIVE 6 and canot find anything in help and web forums either.

#1. At first, I load utility "VectorMatrixFunctions.mth"

#2. when I insert DIV([1/r^2, 0, 0], spherical) I obtain ZERO

But it seems wrong,
f.e. for Gravitation we have divergence for vectors with (1/r^2) and we should expect poisson equation related to volume,
As we know for gravity it is (4 \pi GMm ) / V

What is wrong then with my calculations using Derive 6?

2. Aug 7, 2011

### Bill Simpson

DIV([r,s,t]) gives 0
DIV([x,y,z]) gives 3

so perhaps Derive is expecting your vector in [x,y,z] cartesian form.

DIV([1/x^2,0,0]) gives -2/x^3
DIV([1/(x^2+y^2+z^2),0,0]) gives - 2*x/(x^2 + y^2 + z^2)^2

Last edited: Aug 7, 2011