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MathGroup Archive 1990

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D and Derivative - help please

  • To: mathgroup at yoda.ncsa.uiuc.edu
  • Subject: D and Derivative - help please
  • From: uunet!uthvm1.bitnet!AN123651
  • Date: Thu, 22 Mar 90 12:41:28 CST

I would appreciate some help with this from anyone who understands
Mathematica better than I. Suppose I define a function:

   f[x_,y_] := x + y + Gamma[x,y]

When I take its derivative using D, everything is fine.

   D[f[x,y],x]

            (1,0)
   1 + Gamma     [x, y]

Derivative, on the other hand, can't get as far.

   Derivative[1,0][f]

    (1,0)
   f

Now, suppose I define my own value for the derivative of the
Gamma function.

   Derivative[1,0][Gamma] = Plus

D understands this perfectly, but Derivative not at all.

   D[f[x,y],x]

   1 + x + y

   Derivative[1,0][f]

   (1,0)
   f

   Derivative[1,0][f][x,y]

   (1,0)
   f     [x, y]

What's the difference here? How can I get Derivative to use my
definition?

Thanks for any help.

                               E. Neely Atkinson
                               AN123651 at UTHVM1.BITNET
                               neely at mdaali.cancer.utexas.edu



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