Re: confused about asserting variable is element of Reals
- To: mathgroup at smc.vnet.net
- Subject: [mg103107] Re: confused about asserting variable is element of Reals
- From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
- Date: Tue, 8 Sep 2009 05:58:05 -0400 (EDT)
- References: <h829lj$3tg$1@smc.vnet.net>
Hi Dushan,
The Element operator can be used inside assumption environments or,
for numeric arguments, to test memberships. It does NOT set some kind
of Real property.
One way of using it would be:
Assuming[a \[Element] Reals, Simplify[Im[a]]]
Cheers -- Sjoerd
On Sep 7, 8:36 am, dushan <dush... at spinn.net> wrote:
> 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