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MathGroup Archive 1998

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Re: Mathmatica Problem...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg14355] Re: [mg14320] Mathmatica Problem...
  • From: David Withoff <withoff>
  • Date: Thu, 15 Oct 1998 00:28:57 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

> 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

I am guessing that you are referring to the manual for Version 2.  I
didn't see this example in the Version 3 manual, but you can get this
behavior in Version 3 using TrigReduce:

In[6]:= TrigReduce[Cos[x]^3 Sin[x]^2] //Expand

        Cos[x]   Cos[3 x]   Cos[5 x] Out[6]= ------ - -------- -
--------
          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???

There is a listing "Incompatible Changes in Version 3.0" in Appendix
A.13 of the Mathematica book, which mentions this change in the Trig
option. It is always possible to get Version 2 behavior in Version 3,
and most  functionality that existed in Version 2 is identical or
closely equivalent in Version 3, but there is not a switch that will
cause Version 3 to be identical to Version 2 in every respect.

> Any comments on this would be appreciated.  Also who should I send this
> to at Wolfram?

You can send technical questions, comments, suggestions, etc., to
Wolfram Research technical support at the address support at wolfram.com.

Dave Withoff
Wolfram Research


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