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MathGroup Archive 1997

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Partial Derivatives

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7774] Partial Derivatives
  • From: govinder at Lourie.und.ac.za (Kesh Govinder)
  • Date: Tue, 8 Jul 1997 22:40:55 -0400
  • Organization: University of Natal
  • Sender: owner-wri-mathgroup at wolfram.com

Hi

Does anyone else think that the partial derivative implementation in
Mma is a little weird?   I am trying to find partial derivatives of
an equation, eg y''[x] + y'[x] + x^2 ==0.
What I would like is to say something like pD[eqn,y[x]] and get back 0
while pD[eqn,y''[x]] will give me 1.  Certainly D does this.  However,
I also want pD[eqn,x] to give me 2x and not y'''[x] + y''[x] + 2 x.
Can anyone please suggest a way to get around this?

Note that entering the equation as y'' + y' + x^2 does not work.  Here
D[eqn,y] gives me the strange result y''' + y'' which I really cannot 
understand.

I would really appreciate any help.

Thanks in advance
Kesh

-- 
***************************************************************************
Kesh Govinder
Dept of Maths and App Maths, University of Natal -- Durban, South Africa
Tel:  (+27) 31 260 3021
Fax:  (+27) 31 260 1017
Email: govinder at lourie.und.ac.za              |
       govinder at ph.und.ac.za                  | 
****************************************************************************


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