SphJacobian:

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   This function is the application to the chain rule to a function U
   in spherical coordinates U( r, phi, theta ) such that

   [dU/dx;dU/dy;dU/dZ] = c*[dU/dr;dU/dphi;dU/dtheta]

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   Form:
   c = SphJacobian( x )
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   ------
   Inputs
   ------
   r            (3,1)   Vector
                        
   -------
   Outputs
   -------
   c            (3,3)   Jacobian
                        
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