RE: efficient term collection algorithm
- To: mathgroup at smc.vnet.net
- Subject: [mg69190] RE: [mg69155] efficient term collection algorithm
- From: "David Park" <djmp at earthlink.net>
- Date: Fri, 1 Sep 2006 06:41:31 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Blake,
What about trying to extract the denominators and then using the Mathematica
Collect routine?
collectDenominators[expr_] :=
Module[{work = Expand[expr], factors},
factors = Union[Denominator /@ List @@ work]^-1;
Collect[expr, factors]
]
collectDenominators[(b*i + a*j + c*j)/(i*j)]
(a + c)/i + b/j
David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/
From: Blake Laing [mailto:laing at nhn.ou.edu]
To: mathgroup at smc.vnet.net
Dear Math Group
I wish to combine terms in a expression which share a denominator, such
as in the following simple case:
In[1]:=
a/i+b/j+c/i//.Plus[Times[A_.,Power[denom_,-1]],Times[B_.,Power[denom_,-1]]]:
>
Factor[Plus[A,B]Power[denom,-1]]//InputForm
Out[1]//InputForm=
(a + c)/i + b/j
The actual expression I am working with contains thousands of terms, and
a pairwise algorithm such as this is wholly inadequate. Will one of you
please suggest a more efficient way to combine each additive term in a
large expression with a shared denominator?
Thanks,
Blake Laing
physics grad student
University of Oklahoma