       Re: Collect exponents only

• To: mathgroup at smc.vnet.net
• Subject: [mg101405] Re: [mg101385] Collect exponents only
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Sun, 5 Jul 2009 04:47:47 -0400 (EDT)

```expr = A Exp[I (x + y) - I x] + A^2 Exp[I (x + y) - I y];

expr /. Exp[z_] :> Exp[Simplify[z]]

A^2*E^(I*x) + A*E^(I*y)

Map[Simplify, expr, {2}]

A^2*E^(I*x) + A*E^(I*y)

Bob Hanlon

---- 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?