Re: replacement x->y except in Exp[x]

*To*: mathgroup at smc.vnet.net*Subject*: [mg110851] Re: replacement x->y except in Exp[x]*From*: Leonid Shifrin <lshifr at gmail.com>*Date*: Thu, 8 Jul 2010 07:41:02 -0400 (EDT)

Hi Sebastian, the simplest in such cases is to use a first rule that does nothing when expression is what you don't want to change, Exp[x] in this case: In[1]:= {Sin[x + Exp[x]], Cos[x], x^2} /. {Exp[x] -> Exp[x], x -> y} Out[1]= {Sin[E^x + y], Cos[y], y^2} Be aware though that if you use Replace, this will not work since Replace works from the bottom of the expression: In[2]:= Replace[{Sin[x + Exp[x]], Cos[x], x^2}, {Exp[x] -> Exp[x], x -> y}, Infinity] Out[2]= {Sin[E^y + y], Cos[y], y^2} Here is a more complicated pattern which will work both with ReplaceAll and with Replace: In[3]:= {Sin[x + Exp[x]], Cos[x], x^2} /. h_[left___, x, right___] /; ! (h === Exp && {left} === {} && {right === {}}) :> h[left, y, right] Out[3]= {Sin[E^x + y], Cos[y], y^2} In[4]:= Replace[{Sin[x + Exp[x]], Cos[x], x^2}, h_[left___, x, right___] /; ! ((h === Power) && ({left} === {E}) && ({right} === {})) :> h[left, y, right], Infinity] Out[4]= {Sin[E^x + y], Cos[y], y^2} Regards, Leonid On Thu, Jul 8, 2010 at 11:12 AM, Sebastian <sebhofer at gmail.com> wrote: > Is it possible to exclude certain patterns from replacements? > For example I want to replace y for x everywhere except in Exp[x]. > > TIA Sebastian > >