MathGroup Archive 2011

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Problem with Patterns and Integrate


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



  • Prev by Date: Re: Point light source penetrating through surfaces
  • Next by Date: Manipulate bug (?) when stepping by degrees?
  • Previous by thread: Re: Problem with Patterns and Integrate
  • Next by thread: Re: Problem with Patterns and Integrate