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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