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

*To*: mathgroup at smc.vnet.net*Subject*: [mg53533] Re: [mg53509] Re: [mg53467] Problem with transformation rule of a function -- Another one*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Sat, 15 Jan 2005 21:08:18 -0500 (EST)*References*: <200501150644.BAA25320@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 15 Jan 2005, at 07:44, Alain Cochard wrote: > Thank you so much to those who answered. Now, here is another one. > > The following works as I expect: > > In[1]:= expr=Integrate[D[g[x,t],t],{x,0,1}] > > (0,1) > Out[1]= Integrate[g [x, t], {x, 0, 1}] > > In[2]:= g[x_,t_]:= x f[t] > > In[3]:= expr > > f'[t] > Out[3]= ----- > 2 > > Now I would like to use a transformation rule instead, like in: > > In[1]:= expr=Integrate[D[g[x,t],t],{x,0,1}] ; > > In[2]:= expr/. g[x,t]->x f[t] > > (0,1) > Out[2]= 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 > > > There are several ways. One is expr /. Derivative[0, 1][g][x, t] :> D[x*f[t], t] Derivative[1][f][t]/2 another, which I prefer, is: expr /. g -> Function[{x, t}, x*f[t]] Derivative[1][f][t]/2 Andrzej Kozlowski Chiba, Japan http://www.akikoz.net/~andrzej/ http://www.mimuw.edu.pl/~akoz/

**References**:**Re: Problem with transformation rule of a function -- Another one***From:*Alain Cochard <alain@geophysik.uni-muenchen.de>