Re: Replace in operators
- To: mathgroup at smc.vnet.net
- Subject: [mg102922] Re: [mg102869] Replace in operators
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Wed, 2 Sep 2009 04:03:42 -0400 (EDT)
- References: <200909010750.DAA18607@smc.vnet.net>
I think, you can do on of three things:
1.
Unevaluated[f[x] + D[f[x], x]] /. f[x] -> g[x]
Derivative[1][g][x] + g[x]
or
2.
f[x] + D[f[x], x] /. {f[x] :> g[x], Derivative[1][f][x] :>
Derivative[1][g][x]}
Derivative[1][g][x] + g[x]
3.
f[x] + D[f[x], x] /. f -> g
Derivative[1][g][x] + g[x]
(There are also some variants of 1 and 2 ).
From what you say, it seems that the first choice (wrapping
Unevaluated around the input) is the most suitable.
Andrzej Kozlowski
On 1 Sep 2009, at 09:50, did wrote:
> 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.
>
- References:
- Replace in operators
- From: did <didier.oslo@hotmail.com>
- Replace in operators