Re: Complex Oddity
- To: mathgroup at smc.vnet.net
- Subject: [mg57480] Re: Complex Oddity
- From: Bill Rowe <readnewsciv at earthlink.net>
- Date: Sun, 29 May 2005 01:03:40 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
On 5/28/05 at 5:39 AM, nospamjreed at alum.mit.edu (John Reed) wrote:
>I was trying to separate the real and imaginary parts of a
>complicated expression, and ended up with something strange. Here
>is a short version of what happened.
>Let z = x + I y, then realPart = z /. {Complex[a_,b_]->a} gives
>realPart = x. Great!
>Now, try imagPart = z /. {Complex[a_,b_]->b} returns with imagPart
>= x + y. Oops
>In my original expression, it was harder to see, but the same error
>was occuring.
This isn't an error. To see why consider
In[1]:=
z = x + I*y;
FullForm[z]
Out[2]//FullForm=FullForm[x + Complex[0, 1]*y]
In your first example, the rule Complex[a_,b_]->a replaces the expression Complex[0,1] with 0 and the entire expression becomes x + 0 y which of course is x.
In the second example, Complex[0,1] gets replaced by 1 and of course the expression becomes x + y.
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