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Re: Collecting like terms after TrigReduce

  • To: mathgroup at
  • Subject: [mg108935] Re: Collecting like terms after TrigReduce
  • From: Bob Hanlon <hanlonr at>
  • Date: Wed, 7 Apr 2010 07:26:03 -0400 (EDT)
  • Reply-to: hanlonr at

Use Collect

expr = c1*Cos[w*t] + s1*Sin[2 w*t] + a1 + c2*Cos[2 w*t] + 
   c3*Cos[w*t] + s2*Sin[w*t] + c4*Cos[w*t] + a2 + c4*Cos[2 w*t] + 
   s3 Sin[2 w*t];

Collect[expr, DeleteCases[Variables[expr], _?AtomQ]]

a1 + a2 + (c1 + c3 + c4)*Cos[t*w] + 
   (c2 + c4)*Cos[2*t*w] + 
   (s1 + s3)*Sin[2*t*w] + s2*Sin[t*w]

Bob Hanlon

---- Geico Caveman <spammers-go-here at spam.invalid> wrote: 

I have a large expression that is expressed (after TrigReduce) as a
series of the form:

c1*cos(wt) + s1*sin(2wt) + a1+c2*cos(2 wt) + c3* cos(wt) + s2*sin(wt) +
c4*cos(wt) + a2+c4*cos(2wt) + s3 sin(2wt)

(This is just an illustrative example. The precise number of terms is
larger and the number of each kind, impossible to know ahead of the

Is there any way (for compactness reasons alone) to force Mathematica
to put this in a standard form:

(a1+a2) + (c1+c3) cos(wt) + (c2 + c4)cos (2wt) + s2 sin(wt) + (s1+s3)
sin(2wt) ?

Using Simplify is not an option since that gets rid of the higher
harmonic terms (which I want).

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