Re: Problem with transformation rule of a function

*To*: mathgroup at smc.vnet.net*Subject*: [mg53490] Re: [mg53467] Problem with transformation rule of a function*From*: DrBob <drbob at bigfoot.com>*Date*: Fri, 14 Jan 2005 08:54:38 -0500 (EST)*References*: <16858.22033.555637.91757@localhost.localdomain> <200501130812.DAA03785@smc.vnet.net>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

Your first attempt fails because M[2][t] doesn't actually appear in the expr's derivative term: expr = M[1][ t] + M[2][t] + Integrate[M[1][t], t] + Integrate[M[2][t], t] + D[M[1][t], t] + D[M[2][t], t]; FullForm[expr] FullForm[Integrate[M[1][t], t] + Integrate[M[2][t], t] + M[1][t] + M[2][t] + Derivative[1][M[1]][t] + Derivative[1][M[2]][t]] Look closely, and you'll see where M[2][t] does -- and doesn't -- appear. The second attempt almost works, but this is what you really want: expr //. {M[1] -> f, M[2] -> (0 & )} f[t] + Integrate[f[t], t] + Derivative[1][f][t] 0& is the zero function you meant to use. Bobby On Thu, 13 Jan 2005 03:12:10 -0500 (EST), Alain Cochard <alain at geophysik.uni-muenchen.de> wrote: > I define an expression: > > In[1]:= expr=M[1][t] + M[2][t] + Integrate[M[1][t],t] + Integrate[M[2][t],t] + D[M[1][t],t] + D[M[2][t],t]; > > Out[1]= Integrate[M[1][t], t] + Integrate[M[2][t], t] + M[1][t] + M[2][t] + > > > (M[1])'[t] + (M[2])'[t] > > and then I try 2 transformation rules on this expression: > > In[2]:= vers1=expr/.{M[1][t]->f[t], M[2][t]->0} > > Out[2]= f[t] + Integrate[f[t], t] + (M[1])'[t] + (M[2])'[t] > > In this first one, I get the output I expect for the function and > integration terms, but not for the derivative ones. > > In[3]:= vers2=expr/.{M[1]->f, M[2]->0} > > Out[3]= 0[t] + f[t] + Integrate[0[t], t] + Integrate[f[t], t] + f'[t] > > In this second version, I get these 0[t] terms for the function and > integration terms, with which I further have to deal with to achieve > what I want: > > In[4]:= %/.{0[t]->0} > > Out[4]= f[t] + Integrate[f[t], t] + f'[t] > > > I would first like to understand why the derivation and integration > terms are not treated in an identical way, and then I would like to > know if there is a more elegant way to do what I want in a single > step. > > Thanks in advance, > AC > > > > -- DrBob at bigfoot.com www.eclecticdreams.net

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