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Re: a question about complex variable

• To: mathgroup at smc.vnet.net
• Subject: [mg21661] Re: [mg21620] a question about complex variable
• From: "Richard Finley" <rfinley at medicine.umsmed.edu>
• Date: Fri, 21 Jan 2000 04:00:12 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

Try the following:

In[1]:= FullSimplify[Abs[C], Im[P]==0]
Out[1]:= Abs[Tan[A]]

as it should.  Look in the Mathematica help or book for a description of the Arg[z] function....it returns unevaluated unless z is numeric.    Regards,  RF

>>> ZHU Xiaopeng <xpzhu at red.semi.ac.cn> 01/18/00 01:35AM >>>
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?