Services & ResourcesWolfram ForumsMathGroup Archive

[Date Index] [Thread Index] [Author Index]

Re: Re: Collect exponents only

• To: mathgroup at smc.vnet.net
• Subject: [mg101428] Re: Re: [mg101385] Collect exponents only
• From: Alexei Boulbitch <Alexei.Boulbitch at iee.lu>
• Date: Tue, 7 Jul 2009 05:05:39 -0400 (EDT)

Dear Andrzej,

I realized that I cannot understand, how does one of the methods that you give here work. It is the following:  

Simplify /@ (A*Exp[I*(x + y) - I*x] + A^2*Exp[I*(x + y) - I*y])

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

On what elements do you map Simplify here? I would be grateful for any explanation.

Thank you, Alexei



On 4 Jul 2009, at 19:43, Francisco Rojas 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?
> Thanks in advance,
> Francisco
>


There is a vary large number of ways. For example:

(A*Exp[I*(x + y) - I*x] + A^2*Exp[I*(x + y) - I*y]) /. Exp[p_] :>  
Exp[Simplify[p]]
A^2 E^(I x) + A E^(I y

or

Expand[Simplify[A*Exp[I*(x + y) - I*x] + A^2*Exp[I*(x + y) - I*y]]]
A^2*E^(I*x) + A*E^(I*y)

or

Simplify /@ (A*Exp[I*(x + y) - I*x] + A^2*Exp[I*(x + y) - I*y])

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

or even

Simplify[A*Exp[I*(x + y) - I*x] + A^2*Exp[I*(x + y) - I*y],  
ExcludedForms -> A^2]
A^2*E^(I*x) + A*E^(I*y)

Andrzej Kozlowski


-- 
Alexei Boulbitch, Dr., habil.
Senior Scientist

IEE S.A.
ZAE Weiergewan
11, rue Edmond Reuter
L-5326 Contern
Luxembourg

Phone: +352 2454 2566
Fax:   +352 2454 3566

Website: www.iee.lu

This e-mail may contain trade secrets or privileged, undisclosed or otherwise confidential information. If you are not the intended recipient and have received this e-mail in error, you are hereby notified that any review, copying or distribution of it is strictly prohibited. Please inform us immediately and destroy the original transmittal from your system. Thank you for your co-operation.

• Follow-Ups:
  • Re: Re: Re: Collect exponents only
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>