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MathGroup Archive 1998

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Re: Mathmatica Problem...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg14344] Re: Mathmatica Problem...
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Thu, 15 Oct 1998 00:28:47 -0400
  • References: <6vuqt7$8ju@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Mr D.J. Winstanley wrote in message <6vuqt7$8ju at smc.vnet.net>...
>
>Dear mathgroup,
>
>We have just upgraded to release 3 of mathematica and we  have found a
>problem with the Expand function as described in the mathematica
>manual.  Here is the mathematica 3.0 output...
>
>
>In[3]:= Expand[Cos[x]^3 Sin[x]^2,Trig->True]
>
>gives
>
>              3       2
>Out[3]= Cos[x]  Sin[x]
>
>
>this is not the answer given in the manual, which is...
>
>  Cos[x] - Cos[3 x] - Cos[5 x]
>  ------   --------   --------
>    8         16         16
>
>
>We were led to believe that the new version was compatible with the
>previous version.
>
>Is there a switch to obtain compatibility???
>
>Any comments on this would be appreciated.  Also who should I send this
>to at Wolfram?
>
>thanks for your help
>


David,
I don't have Mathematica 2.2 anymore - can you give the reference to the
manual information that you quote please?

I also get

cs =Cos[x]^3  Sin[x]^2;
Expand[Cos[x]^3  Sin[x]^2,Trig->True]


      3       2
Cos[x]  Sin[x]

But that is what I would expect.


The following two evaluations give the result that you quote from the
manual (up to multiplying out).


TrigReduce[cs]

1
-- (2 Cos[x] - Cos[3 x] - Cos[5 x])
16


Apart[cs,Trig->True]

Cos[x]   1             1
------ - -- Cos[3 x] - -- Cos[5 x]
  8      16            16


----------------------
Allan Hayes
Mathematica Training and Consulting
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565



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