       Re: Collect exponents only

• To: mathgroup at smc.vnet.net
• Subject: [mg101409] Re: [mg101385] Collect exponents only
• From: Leonid Shifrin <lshifr at gmail.com>
• Date: Sun, 5 Jul 2009 04:48:32 -0400 (EDT)
• References: <200907041043.GAA17784@smc.vnet.net>

```Hi Francisco,

one way is to use pattern-matching to simplify only specific expresions:

In:=
A Exp[I (x+y)-I x]+A^2 Exp[I (x+y)-I y]/.x:Power[E,_]:> Simplify[x]

Out = 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?