       Re: Replace in an elegant way

• To: mathgroup at smc.vnet.net
• Subject: [mg122872] Re: Replace in an elegant way
• From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
• Date: Sun, 13 Nov 2011 07:18:20 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201111130943.EAA29993@smc.vnet.net>

```On 13 Nov 2011, at 10:43, Mirko wrote:

> Hi all,
> I have following equation:
>
> ((1 + theta[m])^2)/(1 - m) - lambda*((theta[m] + ((lambda + m -
lambda*m)*(1 + theta[m])*(1 + theta[m] - lambda*theta[m]))/(1 - m) +
>     (m*Derivative[theta][m])/lambda))
>
> I want to replace all m that are not an argument of theta[m] or the
Derivative. However, if I use
> /., it replaces all m. If I use Replace[expr,m->qq] it doesn't replace
anything. (qq is the one I want to replace with). If I specify any
level, it doesn't change anything, unless I use -1, but then I replace
everything.
>
> Do you know how I solve this problem?
> Right now I use:
> //. Derivative[y_][theta][m] -> Derivative[y][theta][dd] //.
>    theta[m] -> theta[dd] /. m -> qq //.
>  Derivative[y_][theta][dd] -> Derivative[y][theta][m] //.
> theta[dd] -> theta[m]
>
> but this is not elegant at all (and takes slightly longer).

expr = ((1 + theta[m])^2)/(1 - m) -
lambda*((theta[
m] + ((lambda + m - lambda*m)*(1 + theta[m])*(1 + theta[m] -
lambda*theta[m]))/(1 - m) + (m*Derivative[theta][m])/
lambda))

expr /. (f : Except[theta | Derivative[theta]])[a___, m, b___] :>
f[a, u, b]

(theta[m] + 1)^2/(1 - u) -
lambda*((u*Derivative[theta][m])/lambda +
((theta[m] + 1)*(-(lambda*theta[m]) + theta[m] +
1)*(lambda*(-m) + lambda + u))/(1 - u) +
theta[m])

Andrzej Kozlowski

```

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