Ask for help with Divergence in Derive 6

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SUMMARY

The forum discussion addresses an issue with the divergence function, DIV, in Derive 6. The user reports that when calculating the divergence of the vector field DIV([1/r^2, 0, 0]) in spherical coordinates, the output is zero, which contradicts expectations based on gravitational theory. The user concludes that Derive 6 may require vectors to be expressed in Cartesian coordinates, as evidenced by successful calculations with DIV([x,y,z]) and DIV([1/x^2,0,0]). This indicates a limitation in the software's handling of spherical coordinates.

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pogono
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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?
 
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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
 
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