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Re: Newby Q: How to specify reals

• To: mathgroup at smc.vnet.net
• Subject: [mg110520] Re: Newby Q: How to specify reals
• From: "David Park" <djmpark at comcast.net>
• Date: Wed, 23 Jun 2010 01:52:00 -0400 (EDT)

When working with complex expressions your best friend is the ComplexExpand
command. For some reason, this command doesn't immediately jump to the
notice of beginners and this leads to frequent questions on MathGroup.

R1 + I 1/(w C1) 
ComplexExpand[Im[%]] 

R1 + I/(C1 w) 

1/(C1 w) 

Mathematica generally assumes all variables are complex. ComplexExpand
assumes that all variables are real, except for ones you specifically
designate as complex. It is worth studying the Help page for ComplexExpand.
The TargetFunctions option is often useful.


David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/  


From: DBird [mailto:dbird at ieee.org] 


Trying the following procedure:

In[41]:= {T1, T2, C1, C2, R1, R2, w} \[Element] Reals

Out[41]= (T1|T2|C1|C2|R1|R2|w)\[Element]\[DoubleStruckCapitalR]

In[42]:= x = R1 + I 1/(w C1)

Out[42]= R1+I/(C1 w)

In[43]:= Im[x]

Out[43]= Re(1/(C1 w))+Im(R1)

Question is, how do I specify the list {T1,T2,...} such that Im[x]
yield just R1.

I usually find I am missing something dumb...

Thanks,

Dave