Re: Partial Derivatives
- To: mathgroup at smc.vnet.net
- Subject: [mg7821] Re: Partial Derivatives
- From: Paul Abbott <paul at physics.uwa.edu.au>
- Date: Mon, 14 Jul 1997 03:01:07 -0400
- Organization: University of Western Australia
- Sender: owner-wri-mathgroup at wolfram.com
Kesh Govinder wrote: > 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. D is perfectly well implemented and works fine! However, I assume that you are trying to solve a variational problem and need variational derivatives? If so then have a look at the Calculus`VariationalMethods` package which includes VariationalD and other related operators. This should do what you want. Cheers, Paul ____________________________________________________________________ Paul Abbott Phone: +61-8-9380-2734 Department of Physics Fax: +61-8-9380-1014 The University of Western Australia Nedlands WA 6907 mailto:paul at physics.uwa.edu.au AUSTRALIA http://www.pd.uwa.edu.au/Paul God IS a weakly left-handed dice player ____________________________________________________________________