MathGroup Archive 1997

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

Search the Archive

Re: trig expansion


On 30 Sep 1997 19:05:29 -0400, in comp.soft-sys.math.mathematica you
wrote:

>How can I cause Mathematica to expand Sin[2 Pi omega t + 2 Pi delta],
>where delta and omega are symbols, into the form
>
>   Cos[2 Pi delta] Sin[2 Pi omega t] + Sin[2 Pi delta] Cos[2 Pi omega t]
>
>without using a replacment rule=20
>
>    Sin[a_ + b_] -> Sin[a]Cos[b] + Cos[a]Sin[b]
>
>explicitly?  (No TrigExpand does NOT do the trick -- it expands all
>the way down to trig functions of Pi delta and Pi t omega!)

Here's a solution that appears to be a bit more general than those I've
seen posted so far. The notion is to temporarily denature Times to foil
TrigExpand:


In[40]:=3D TrigExpand[Sin[a x + b y + c d z]
             /.HoldPattern[Times[p__]]:>TimesHold[p]]
           /.TimesHold[p__]:>Times[p]
Out[40]=3D
Cos[b y] Cos[c d z] Sin[a x]+Cos[a x] Cos[c d z] Sin[b y]+
  Cos[a x] Cos[b y] Sin[c d z]-Sin[a x] Sin[b y] Sin[c d z]
Tom Burton


  • Prev by Date: Re: prograMing: split a list
  • Next by Date: Integrate got slower in Version 3.0/Example
  • Previous by thread: Re: trig expansion
  • Next by thread: Re: trig expansion