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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)
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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>