       Re: Re: Problem with transformation rule of a function -- Another one

• To: mathgroup at smc.vnet.net
• Subject: [mg53528] Re: [mg53509] Re: [mg53467] Problem with transformation rule of a function -- Another one
• From: DrBob <drbob at bigfoot.com>
• Date: Sat, 15 Jan 2005 21:08:05 -0500 (EST)
• References: <200501150644.BAA25320@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```expr = HoldForm@Integrate[D[g[x, t], t], {x, 0, 1}];
expr /. g[x, t] -> x f[t] // ReleaseHold

f'[t]/2

Bobby

On Sat, 15 Jan 2005 01:44:08 -0500 (EST), Alain Cochard <alain at geophysik.uni-muenchen.de> wrote:

> Thank you so much to those who answered.  Now, here is another one.
>
> The following works as I expect:
>
>      In:= expr=Integrate[D[g[x,t],t],{x,0,1}]
>
> 			(0,1)
>      Out= Integrate[g     [x, t], {x, 0, 1}]
>
>      In:= g[x_,t_]:= x f[t]
>
>      In:= expr
>
> 	     f'[t]
>      Out= -----
> 	       2
>
> Now I would like to use a transformation rule instead, like in:
>
>      In:= expr=Integrate[D[g[x,t],t],{x,0,1}] ;
>
>      In:= expr/. g[x,t]->x f[t]
>
> 			(0,1)
>      Out= Integrate[g     [x, t], {x, 0, 1}]
>
> I tried various alternatives (with "//", ":>", "Evaluate", using "_"
> or not, with "Hold/ReleaseHold" -- although not in a fully systematic
> way, I admit) without success.  Is it feasible?
>
> Thanks,
> Alain
>
>
>
>
>

--
DrBob at bigfoot.com
www.eclecticdreams.net

```

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