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Re: Pattern matching partial derivatives

• To: mathgroup at smc.vnet.net
• Subject: [mg52422] Re: Pattern matching partial derivatives
• From: Nicolas Girard <nicolas.girard at strasbourg.fr>
• Date: Fri, 26 Nov 2004 06:20:28 -0500 (EST)
• References: <co4dsi$l82$1@smc.vnet.net> <co6hoe$nq3$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Le Fri, 26 Nov 2004 06:16:46 +0000, David Bailey a écrit :
> Nicolas,
> 
> Yes, getting this output from Mathematica can be a sign of damnation!
> 
> Alternatively, look at this:
> 
> D[f_, x_, Rule[NonConstants, nc_]] // FullForm
> 
> 0
> 
> If you want to manipulate derivatives in complicated ways, one way is to 
> use your own notation for a derivative (say dD) which will obviously not 
> evaluate, and then use dD ->D to get evaluation when you need it.
> 
David,
thanks much for the tip, it appears to do the job indeed...
still I'm frustrated. Why couldn't we use patterns to manipulate partial
derivatives ? How can it be that, as you pointed out,

   D[f_, x_, Rule[NonConstants, nc_]] // FullForm

gives 0 ? This seems crazy to me...