       Re: Collect exponents only

• To: mathgroup at smc.vnet.net
• Subject: [mg101397] Re: [mg101385] Collect exponents only
• From: "David Park" <djmpark at comcast.net>
• Date: Sun, 5 Jul 2009 04:46:21 -0400 (EDT)
• References: <22897006.1246704619067.JavaMail.root@n11>

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

expr /. Exp[s_] :> Simplify[Exp[s]]
A^2 E^(I x) + A E^(I y)

Collect[expr, A, Simplify]
A^2 E^(I x) + A E^(I y)

David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/

From: Francisco Rojas [mailto:fjrojas at gmail.com]

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?