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ComplexExpand

• To: mathgroup at yoda.physics.unc.edu
• Subject: ComplexExpand
• From: Elliot Weinberg <weinberg at symcom.math.uiuc.edu>
• Date: Thu, 10 Feb 1994 09:08:15 -0600

The following peculiar phenomena seems to be special to
certain installations of Mathematica.  I can reproduce it
on the logins of some of my colleagues, but not on others.
Nor does this happen on my personal copy for a MacIntosh.
The Wolfram people have not been able to locate the 
difficulty; it does not arise on any of their versions.

I write to ask if anyone else can reproduce the problem
or suggest the solution.  ComplexExpand behaves strangely
on my Sparc station unless it is 'initialized' by first
evaluating it in a specific case.  Here is an example.

I ask to expand Exp[I x] and get the wrong answer:

mira:::math
Mathematica 2.2 for SPARC
Copyright 1988-93 Wolfram Research, Inc.

In[1]:= ComplexExpand[Exp[I x]]

Out[1]= 1

In[2]:= Exit

Starting a brand new session I can get the correct result
by first asking to evaluate an expression which yields
a nonsymbolic result.


mira:::math
Mathematica 2.2 for SPARC
Copyright 1988-93 Wolfram Research, Inc.

In[1]:= ComplexExpand[Exp[Pi I]]

Out[1]= -1

In[2]:= ComplexExpand[Exp[I x]]

Out[2]= Cos[x] + I Sin[x]


I stumbled across this phenomena when reviewing a program I
use in a symbolic algebra course.  It ran fine last summer
under 2.1, but blows up for me in 2.2.  ComplexExpand was
used in an incidental way, so it took a while for me to figure
out the source of my difficulty.  The examples above use
ComplexExpand in a way different from that used in the program,
but clearly illustrate that something strange is happening.