TrigReduce: controlling the scope

*To*: mathgroup at smc.vnet.net*Subject*: [mg129061] TrigReduce: controlling the scope*From*: alan <alansbarnett at verizon.net>*Date*: Tue, 11 Dec 2012 02:25:05 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net

I have an expression that is a sum of products of trignometric functions. Each term is something like this: Sin[alpha] Cos[omega tau1] Cos[omega tau2] Cos[beta]. (1) I want to apply trig identities to the terms that contain omega to transform them into trig functions of sums and differences, but I don't want the same transformation applied to the terms involving alpha and beta. For example, I want to express (1) as (1/2) Sin[alpha] Cos[beta](Cos[omega(tau1 - tau2)]+Cos[omega(tau1 + tau2)]) If I apply TrigReduce to (1), I get terms like Cos[omega tau1 - omega tau2 + alpha - beta]. How do I restrict the action of TrigReduce to terms containing omega? (I can do a hybrid calculation by cutting and pasting the terms I want, but I'd rather not have to cut and paste by hand). Thanks.

**Follow-Ups**:**Re: TrigReduce: controlling the scope***From:*Bob Hanlon <hanlonr357@gmail.com>

**Re: TrigReduce: controlling the scope***From:*Christoph Lhotka <christoph.lhotka@fundp.ac.be>