Re: Collect exponents only

• To: mathgroup at smc.vnet.net
• Subject: [mg101425] Re: [mg101385] Collect exponents only
• From: Francisco Rojas Fernández <fjrojas at gmail.com>
• Date: Tue, 7 Jul 2009 05:05:06 -0400 (EDT)
• References: <200907041043.GAA17784@smc.vnet.net>

```Thanks guys for all your help. I'm new in Mathematica and it is really a
great start to know that you guys are so willing to help.
Best to all
-Francisco

On Sat, Jul 4, 2009 at 4:18 PM, Leonid Shifrin <lshifr at gmail.com> wrote:

> Hi Francisco,
>
> one way is to use pattern-matching to simplify only specific expresions:
>
> In[1]:=
> A Exp[I (x+y)-I x]+A^2 Exp[I (x+y)-I y]/.x:Power[E,_]:> Simplify[x]
>
> Out[1] = A^2*E^(I*x) + A*E^(I*y)
>
> Regards,
> Leonid
>
>
>
>
> On Sat, Jul 4, 2009 at 3:43 AM, Francisco Rojas <fjrojas at gmail.com> wrote:
>
>> Hello,
>>
>> I was wondering if there's anyway to ask the command Simplify (or
>> maybe some other command) to only collect terms in the exponents of a
>> long expression (which contains complex exponentials by the way) and
>> not perform any other kind of simplification.
>>
>> For example I have an expression like this:
>>
>> A Exp[ I (x+y) - I x] + A^2 Exp[ I (x+y) - I y]           ( I is the
>> the imaginary unit )
>>
>> Mathematica does two simplications here: it simplifies the terms in
>> the exponents and factors out the A giving:
>>
>> A (Exp[ I y] + Exp[I x])
>>
>> whereas I would like to obtain only the exponents simplification,
>> i.e.   A^2 Exp[ I y] + A Exp[ I x]
>>
>> Anybody knows how to do this?