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Re: Problem with Patterns and Integrate

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]


Bob Hanlon

On Mon, Nov 28, 2011 at 5:53 AM, Jack McInerney <ejmcinerney at> 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

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