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