Re: How to Extract a common factor from a Sum
- To: mathgroup at smc.vnet.net
- Subject: [mg12971] Re: [mg12882] How to Extract a common factor from a Sum
- From: BobHanlon at aol.com
- Date: Sun, 28 Jun 1998 02:51:57 -0400
- Sender: owner-wri-mathgroup at wolfram.com
Frank,
Try this:
expr = Sum[a*f[k], {k, 1, N}];
factorSum = Sum[(const_)*(term_),
{iter_, low_:1, hi_}] /;
FreeQ[const, iter] :>
const*Sum[term, {iter, low, hi}];
expr /. factorSum
Sum[a*b*f[k]*x^k, {k, N}] //. factorSum
Bob Hanlon
In a message dated 6/24/98 5:41:11 AM, loewenthal at iap.unibe.ch wrote:
>I have a symbolical sum like
>
>expr = Sum[ a f[k], {k,1,N}] and I want to force Mathematica to write
>this as
>expr = a Sum[f[k], {k,1,N}]
>
>What ever I tried it did not work.
>Does anyone knows a solution?