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Re: a question about complex variable
*To*: mathgroup at smc.vnet.net
*Subject*: [mg21651] Re: a question about complex variable
*From*: Harald Giese <giese at dkrz.de>
*Date*: Fri, 21 Jan 2000 04:00:00 -0500 (EST)
*Organization*: Institut fuer Meereskunde, Universitaet Hamburg
*References*: <200001170343.WAA13446@smc.vnet.net> <8615hh$jtk@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
ZHU Xiaopeng wrote:
>
> In my algebra computation, I obtain a expression:
> C = (- I Cos[2 P] - Sin[2 P]) Tan[A]
> P,A are real variables. Apperently, the argument of C is -2(P+Pi/4) and the
> absolute value of C is Tan[A]. But when I use Arg[C] and Abs[C], Mathematica
> tells me:
>
> Out[41]=Abs[(-I Cos[2 P] - Sin[2 P]) Tan[A]]
> Out[42]=Arg[(-I Cos[2 P] - Sin[2 P]) Tan[A]]
>
> This problem appeared at beginning of the computation. I have no idea to deal
> with it, so the expressions become longer and longer during the computation.
> Can somebody help me?
Hi,
You have to tell Mathematica the property within the expression:
Simplify[Abs[C], {P, A} \[Element] Reals]
or
Simplify[Arg[C], {P, A} \[Element] Reals].
But in your case to no avail, even for "A" being real:
In[]:= Simplify[Tan[(2 n - 1) Pi/2], n \[Element] Integers && n > 1]
Out[]= ComplexInfinity
Remark: user defined variables should not start with capital letters,
because they may conflict with predefined Mathematica variables; e.g. C:
"C[i] is the default form for the i-th constant of integration produced
in solving a differential equation with DSolve. "
Regards,
Harald
--- This message was entirely written using recycled electrons ---
Harald Giese
Email: giese at dkrz.de
Phone: +49 (0)40 42838 5796; Fax: +49 (0)40 5605724
Institut fuer Meereskunde der Universitaet Hamburg
(Institute of Oceanography of the University of Hamburg)
Troplowitzstrasse 7, D-22529 Hamburg
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