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