Re: Slow ReIm
- Subject: [mg3405] Re: Slow ReIm
- From: danl (Daniel Lichtblau)
- Date: 4 Mar 1996 10:03:45 -0600
- Approved: usenet@wri.com
- Distribution: local
- Newsgroups: wri.mathgroup
- Organization: Wolfram Research, Inc.
- Sender: daemon at wri.com
In article <4h13tr$rr4 at dragonfly.wolfram.com> Donald Darling <ddarling at math.uci.edu> writes: > Can someone tell me why, after I load the package ReIm and declare the > variables z and u real, it takes over 15 minutes to evaluate > Re[(1- I u z)/(1-2 I u z - z^2)] ? > > Thanks ... Don Darling. > Cannot answer this one directly. But I note that you can get much faster results with: In[3]:= ComplexExpand[Re[(1- I u z)/(1-2 I u z - z^2)], z] // InputForm Out[3]//InputForm= ((1 + u*Im[z])*(1 + 2*u*Im[z] + Im[z]^2 - Re[z]^2))/ Abs[1 - 2*I*u*z - z^2]^2 or, if you do not want to see Abs/Arg, In[4]:= ComplexExpand[Re[(1- I u z)/(1-2 I u z - z^2)], z, TargetFunctions->{Re, Im}] // InputForm Out[4]//InputForm= ((-2*u*Re[z] - 2*Im[z]*Re[z])^2 + (1 + 2*u*Im[z] + Im[z]^2 - Re[z]^2)^2) \ + ((1 + u*Im[z])*(1 + 2*u*Im[z] + Im[z]^2 - Re[z]^2))/ ((-2*u*Re[z] - 2*Im[z]*Re[z])^2 + (1 + 2*u*Im[z] + Im[z]^2 - Re[z]^2)^2) Daniel Lichtblau Wolfram Research, Inc danl at wolfram.com