Re: Q: pattern in list of derivatives
- To: mathgroup at smc.vnet.net
- Subject: [mg22722] Re: Q: pattern in list of derivatives
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Fri, 24 Mar 2000 03:27:04 -0500 (EST)
- Organization: Universitaet Leipzig
- References: <8b9n7a$997@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
you just forgot to wrote two underscores in the Derivative[__][u][__]
pattern.
Cases[{a D[u[x, y], x, x] + c D [u[x, y], y, y]},
Derivative[__][u][__], Infinity]
works fine.
Regards
Jens
Klaus Duellmann wrote:
>
> Dear Mathgroup Member,
>
> I can extract all derivatives from
>
> e.g. s1 = a u'[x] + a u''[x]
>
> by Cases[{s1}, Derivative[_][u][x],-1] and get
>
> {u'[x],u''[x]}
>
> But for mixed derivatives
>
> e.g. {a u[x,y]^(0,1) + c u[x,y]^(1,1)}
>
> the correponding command Cases[{s1}, Derivative[_][u][x,y],-1]
> doesn't work and I receive only the empty list {}.
>
> Any help is much appreciated!
>
>
> Klaus Duellmann
> Mannheim University
>
> E-mail: k.duellmann at uni-mannheim.de