Re: Q: pattern in list of derivatives
- To: mathgroup at smc.vnet.net
- Subject: [mg22746] Re: [mg22696] Q: pattern in list of derivatives
- From: "David Park" <djmp at earthlink.net>
- Date: Fri, 24 Mar 2000 03:27:41 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
Klaus,
The Mathematica display format for mixed derivatives is misleading and I don't think
you can enter them that way. (Perhaps someone will correct me if I am wrong on this.)
So enter:
s1 = a Derivative[0, 1][u][x, y] + c Derivative[1, 1][u][x, y] or
s1 = a D[u[x, y], y] + c D[u[x, y], x, y]
Then your Cases statement needs a double underbar to pick out one or more mixed
derivatives.
Cases[s1, Derivative[__][u][x, y], -1]
{Derivative[0, 1][u][x, y], Derivative[1, 1][u][x, y]}
I pasted the above in InputForm, but Mathematica actually displays it in the notation
you were attempting to use.
David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/
>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
>
>