Date: Mar 24, 2013 4:16 AM
Author: Bob Hanlon
Subject: Re: Integrate with unknow function
If g is the indefinite integral of a contrinuous function f[x] then

Using a replacement rule

ClearAll[f, g, expr];

expr = Integrate[f[d], {d, 0, 3}] -

Integrate[f[d], {d, 0, 2}];

expr /. Integrate[f[x_], {x_, a_, b_}] ->

g[b] - g[a]

-g[2] + g[3]

Alternatively, defining an upvalue for f (TagSet)

ClearAll[f, g, expr];

expr = Integrate[f[d], {d, 0, 3}] -

Integrate[f[d], {d, 0, 2}];

f /: Integrate[f[x_], {x_, a_, b_}] =

g[b] - g[a];

expr

-g[2] + g[3]

Bob Hanlon

On Sat, Mar 23, 2013 at 3:25 AM, Shan <shan.pub@gmail.com> wrote:

> Hi,

>

> I have a very rookie question as follows:

>

> Integrate[f[d], {d, 0,3}] - Integrate[f[d], {d, 0,2}]

>

> How can I get the result as f[d]? Thanks very much for any help!

>

> shan

>