Re: how do you prevent numerator expansion when using 'Together'?
- To: mathgroup at smc.vnet.net
- Subject: [mg122316] Re: how do you prevent numerator expansion when using 'Together'?
- From: Alexei Boulbitch <Alexei.Boulbitch at iee.lu>
- Date: Tue, 25 Oct 2011 06:15:55 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
Hi,
You also can try the following. Assume that you have your complex expression instead of this
expr = 1/(d*g)*(a*g + b*g + a*e + b*e + a*f + b*f)
(a e + b e + a f + b f + a g + b g)/(d g)
simple one. The third part of it is the numerator:
expr[[3]]
a e + b e + a f + b f + a g + b g
This can be also seen by the TreeForm. Then let us factor it:
MapAt[Factor, expr, {3}]
((a + b) (e + f + g))/(d g)
I hope this helps.
Best, Alexei
DrMajorBob wrote:
> Factor[(a + b)/d + ((a + b)*(e + f))/(d*g)]
>
> ((a + b) (e + f + g))/(d g)
>
> Together[(a + b)/d + ((a + b)*(e + f))/(d*g)]
>
> ((a + b) (e + f + g))/(d g)
>
>
Yes, this simplified example does this on my system too, but the actual
expression I have behaves the way I described. Your counter-example
indicates there must be something in my actual expression that causes
the behavior. I'll experiment to see what that might be. Thanks for
pointing this out.
- Dushan
> On Sat, 22 Oct 2011 05:07:37 -0500, Dushan Mitrovich <dushanm at nnips.net>
> wrote:
>
>> I'm using Mathematica 8. When using 'Together' on an expression the
>> numerator
>> is always expanded, complicating the appearance of the final result:
>>
>> In: Together[ (a+b)/d + ((a+b)*(e+f))/(d*g) ]
>> Out: 1/(d*g) * (a*g + b*g + a*e + b*e + a*f + b*f)
>>
>> Instead, I'd much prefer the simpler form
>> 1/(d*g) * (a+b)*(g+e+f)
>>
>> What do I need to do to get the latter form? Thanks.
>>
>> - Dushan
>> [ reverse the middle word of address to reply ]
>>
>
>
Alexei BOULBITCH, Dr., habil.
IEE S.A.
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