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Ask for help with Divergence in Derive 6

  1. Aug 7, 2011 #1
    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. jcsd
  3. Aug 7, 2011 #2
    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
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