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Re: declaring variables


dh61 at rs3.hrz.th-darmstadt.de (Burkhardt Goedde) wrote:

>Dear math users,
>just a simple problem, but I got no answer from thew book.
>Re[x + I y] gives
>Re[x + I y]
>whereas 
>Re[2 + 3 I]
>gives 2
>How could I tell Mathematica that x and y are real numbers?

There is a package <<Algebra`ReIm` that lets you specify that given 
variables are purely real. Try the following:

In[5]:= Needs["Algebra`ReIm`"]

        Im[x]^=0;  

        Im[y]^=0;

        Re[x + I y]

        Im[x + I y]

Out[8]= x
Out[9]= y

The up definitions make the assignment associated with x and y rather
than
with Im...

Hope this helps
Vicki

________________________________________________________________________

 Victoria Steblina                      Email: vvs124 at rsphy1.anu.edu.au
 Optical Sciences Centre                Tel:   61 6 249 5129
 Australian National University         Fax:   61 6 249 5184


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