Re: How to Extract a common factor from a Sum
- To: mathgroup at smc.vnet.net
- Subject: [mg12963] Re: How to Extract a common factor from a Sum
- From: colin at tri.org.au (Colin Rose)
- Date: Sun, 28 Jun 1998 02:51:52 -0400
- Organization: Theoretical Research Institute
- References: <6mq9k4$2pi@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
loewenthal at iap.unibe.ch (Frank Loewenthal) 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? How about MyRule := Sum[u_. w_,{k_,a_,b_}] :> u Sum[w,{k,a,b}] /; FreeQ[u,k]==True Example: In[] expr = Sum[a b c f[k], {k, 1, n}]; In[] expr //. MyRule Out[] a b c Sum[f[k], {k, 1, n}] Hope this helps Cheerio Colin Colin Rose tr(I) - Theoretical Research Institute __________________________________________ colin at tri.org.au http://www.tri.org.au/