Re: confused about asserting variable is element of Reals
- To: mathgroup at smc.vnet.net
- Subject: [mg103098] Re: [mg103084] confused about asserting variable is element of Reals
- From: "David Park" <djmpark at comcast.net>
- Date: Tue, 8 Sep 2009 05:56:27 -0400 (EDT)
- References: <17376327.1252306110063.JavaMail.root@n11>
One approach is to use ComplexExpand, which assumes that any symbols are
zero.
ComplexExpand[Im[a]]
0
ComplexExpand[a^2 - Re[a]^2]
0
But you can include a list of variables that are to be taken as complex.
ComplexExpand[Im[a], {a}]
Im[a]
David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/
From: dushan [mailto:dushanm at spinn.net]
I'm still learning Mathematica (using 7.0.1) and don't understand
Mathematica's response. After finally finding out how to assert that a
variable is real, I tried to verify this by asking Mathematica to show me
that
it knew the imaginary part of the variable is zero. But I couldn't
find a way to do that.. Here're my instructions:
In[1]:= a (ESC)el(ESC) Reals
Out[1]:= a (the element-of symbol) Reals
In[2]:= ##Im[a]
Out[2]:= Im[a]
where '##' is any of {null, Refine[, Simplify[, FullSimplify[}. I
also tried some other combinations, such as 'a^2 - Re[a]^2', but these
didn't help either.
What am I doing wrong? How do I verify such things?
Thanks.
- Dushan Mitrovich