       Re: Integrate with unknow function

• To: mathgroup at smc.vnet.net
• Subject: [mg130228] Re: Integrate with unknow function
• From: Bob Hanlon <hanlonr357 at gmail.com>
• Date: Sun, 24 Mar 2013 04:16:25 -0400 (EDT)
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• References: <20130323072511.390976A2E@smc.vnet.net>

```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 + g

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 + g

Bob Hanlon

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

```

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