Re: How to force ( Exp[I x]/2+Exp[-I x]/2=cos(x) ) ?
- To: mathgroup at smc.vnet.net
- Subject: [mg3430] Re: [mg3402] How to force ( Exp[I x]/2+Exp[-I x]/2=cos(x) ) ?
- From: Dave Snead <76300.3545 at compuserve.com>
- Date: Thu, 7 Mar 1996 02:23:15 -0500
- Sender: owner-wri-mathgroup at wolfram.com
yjtsai at leland.Stanford.EDU (Yeou-Jyh Tsai) writes
> Hello,
>
> I use Mathematica's MatrixExp to generate the symbolic form of
> a matrix's exponential. It gives me lots of
> I x -I x -I x I x
> E E I E IE
> --- + ------ and -------- - -----
> 2 2 2 2
> which should be converted to Cos[x] and Sin[x], respectively. Does anyone
> know how to do this ?
>
> Thanks a lot!
>
> Yeou-Jyh Tsai
> tsai at relgyro.stanford.edu
Try ComplexExpand; it assumes all variables are real.
In[10]:= {Exp[I x]/2 + Exp[-I x]/2, I Exp[-I x]/2 - I Exp[I x]/2} //
ComplexExpand
Out[10]= {Cos[x], Sin[x]}
Good Luck,
Dave Snead
76300.3545 at compuserve.com
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