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
>
>
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