Re: Q: pattern in list of derivatives
- To: mathgroup at smc.vnet.net
- Subject: [mg22754] Re: Q: pattern in list of derivatives
- From: Brian Higgins <bghiggins at ucdavis.edu>
- Date: Fri, 24 Mar 2000 03:27:54 -0500 (EST)
- References: <8b9n7a$997@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Klaus, I think the problem is how you define a mixed derivative> Consider the following: s3 = a D[u[x, y], y] + c D[u[x, y], {x, y}] Cases[{s3}, Derivative[_, _][u][x, y], -1] gives {Derivative[0, 1][u][x, y], Derivative[y, 0][u][x, y]} Cheers, Brian In article <8b9n7a$997 at smc.vnet.net>, Klaus Duellmann <k.duellmann at uni-mannheim.de> 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 > > Sent via Deja.com http://www.deja.com/ Before you buy.