Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2007
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2007

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Combining Fractions with Identical Denominator?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg81043] Re: Combining Fractions with Identical Denominator?
  • From: Valeri Astanoff <astanoff at gmail.com>
  • Date: Sat, 8 Sep 2007 04:01:53 -0400 (EDT)
  • References: <fbqq2m$6p4$1@smc.vnet.net>

On 7 sep, 08:11, "Jung-Tsung Shen" <jus... at gmail.com> wrote:
> I have a sum of a series of fractions (symbolic) of about 50 terms.
> How can I have Mathematica to sum up those with the same denominator?
> By inspection, there are about 5 different denominators. I have wrote
> a simple rule to compare the denominator term by term, but it's rather
> slow. Moreover, sometimes the denominators differ only with a +/-
> sign, a numerical factor (say, 1/2), or a complex i.
>
> In mathematical terms, I have a series in the following form (the
> number of terms can vary):
>
> N1/D1 + N2/D2 + ... + N50/D50
>
> These Di's form 5 different groups. Within each group, there are
> proportional to each other. How could I sum up this series such that
> those terms with Di in the same group is summed?
>
> Thanks for any input.
>
> JT

Good day,

I would use "Collect" this way (example):

In[1]:=ff = n1/(d1 + d2) + n2/d3 + n3/(2*d3) + (n4 + n5)/(I*(d1 +
d2));

In[2]:=dd = List @@ Denominator[Together[ff]]

Out[2]={2, d1 + d2, d3}

In[3]:=Collect[ff, dd]

Out[3]=(n2 + n3/2)/d3 + (n1 - I*(n4 + n5))/(d1 + d2)


V.Astanoff



  • Prev by Date: Re: [Mathematica 6.0.1] Confusing documentation on ColorData,
  • Next by Date: using FindMinimum and FindRoot with "numerically defined" functions
  • Previous by thread: Re: Combining Fractions with Identical Denominator?
  • Next by thread: Re: Combining Fractions with Identical Denominator?