MathGroup Archive 2009

[Date Index] [Thread Index] [Author Index]

Search the Archive

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




  • Prev by Date: Re: Equations over Domains with Mathematica 4?
  • Next by Date: Re: Optimizing a function with a list as a parameter
  • Previous by thread: Re: confused about asserting variable is element of Reals
  • Next by thread: Re: confused about asserting variable is element of Reals