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Replace in operators

• To: mathgroup at smc.vnet.net
• Subject: [mg102869] Replace in operators
• From: did <didier.oslo at hotmail.com>
• Date: Tue, 1 Sep 2009 03:50:26 -0400 (EDT)

I can't figure out how to force Mathematica to replace
f[x] by g[x] in expressions involving operators.
For example:

f[x] + D[f[x],x] /. f[x] -> g[x]

f is not replaced in the derivative. I found
somewhere in the manual that the replacement
does not work on operators, but then it does
not indicate how to do it.

In my real problem, f[x]->g[x] is a (long)
list of complicated transformations resulting
from the resolution of many equations.
Thus, changing f[x]->g[x] by f->g is not
an option.

f[x] + D[f[x],x] is actually a complicated
expression involving many operators.

There are no ways I can do the
substitution by hand, bit by bit.

Any suggestions ?
Thanks

PS: it may help to precise the context.
I'm trying to solve a system of PDEs by
a small parameter expansion. Solving the
system at order N, I want to re-inject the
results into the equations at order N+1.

• Follow-Ups:
  • Re: Re: Replace in operators
    • From: "Elton Kurt TeKolste" <tekolste@fastmail.us>
  • Re: Replace in operators
    • From: Leonid Shifrin <lshifr@gmail.com>
  • Re: Replace in operators
    • From: Jaebum Jung <jaebum@wolfram.com>
  • Re: Replace in operators
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>
  • Re: Replace in operators
    • From: "Elton Kurt TeKolste" <tekolste@fastmail.us>
  • Re: Replace in operators
    • From: Patrick Scheibe <pscheibe@trm.uni-leipzig.de>