Re: Problem with Patterns and Integrate

*To*: mathgroup at smc.vnet.net*Subject*: [mg123275] Re: Problem with Patterns and Integrate*From*: Jack McInerney <ejmcinerney at gmail.com>*Date*: Wed, 30 Nov 2011 03:19:44 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201111281053.FAA19741@smc.vnet.net> <jb2i4f$5ho$1@smc.vnet.net>

On Nov 29, 4:10 am, Bob Hanlon <hanlonr... at gmail.com> wrote: > Compare Rule with RuleDelayed > > func -> Integrate[func, x] > > func -> func*x > > func :> Integrate[func, x] > > func :> Integrate[func, x] > > expr = D[f[x], x]; > > expr /. func_ :> Integrate[func, x] > > f[x] > > Bob Hanlon > > > > > > > > On Mon, Nov 28, 2011 at 5:53 AM, Jack McInerney <ejmciner... at gmail.com> wrote: > > There is something about using patterns that I don't understand, and > > am hoping someone can shed some light. Here is an example of my > > problem. Say I have a function f[x] and I take the derivative of it. > > I can then integrate it and get f[x] back: > > > In[167]:= expr = D[ f[x], x ] > > Out[167]= f=E2=80=B2[x] > > > In[168]:= Integrate[expr, x] > > Out[168]= f[x] > > > If I use a ReplaceAll and a pattern to do the integration, the > > Integrate function treats f'[x] as a constant and returns the wrong > > answer: > > > In[169]:= expr /. func_ -> Integrate[func,x] > > Out[169]= x f=E2=80=B2[x] > > > Any thoughts as to what I am doing wrong? > > > Jack Thanks everyone for the suggestions. I have never been that clear on when I should use RuleDelayed versus Rule. The distinction is much clearer now. Jack

**References**:**Problem with Patterns and Integrate***From:*Jack McInerney <ejmcinerney@gmail.com>