Re: Algebra on complex expressions: Collect

• To: mathgroup at smc.vnet.net
• Subject: [mg15235] Re: Algebra on complex expressions: Collect
• From: "Allan Hayes" <hay at haystack.demon.co.uk>
• Date: Sun, 27 Dec 1998 03:58:28 -0500
• References: <75q17d\$229@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Shawn,

ComplexExpand[1/(a+b I), TargetFunctions->{Re,Im}]

a/(a^2 + b^2) - (I*b)/(a^2 + b^2)

---------------------
Allan Hayes
Mathematica Training and Consulting
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

Ross, Sean wrote in message <75q17d\$229 at smc.vnet.net>...
>
>Does anyone know a way to have a Collect -like function work on
>expressions with complex numbers?  If I have an expression with "x" in
>it, I can use Collect[expr,x], but if I have an expression with "I" in
>it, Collect[expr,I] does not separate the expression into a part with
>and without "I" which would be equivalent to separating the expression
>into real and imaginary parts given all symbols were real.
>
>The RealOnly package does not seem to apply as it excludes imaginary
>numbers alltogether.  ComplexExpand results in a ridiculous amount of
>complexity and is worse than nothing for this purpose.  Expanding and
>multiplying numerator and denominator separately by the complex
>conjugate of the denominator is tedious to do manually and results in
>the same problem of no way to neatly separate the real and imaginary
>parts of a symbolic expression given that all symbols are real.
>
>Thanks.
>
>Sean Ross
>
>Please reply to rosss at plk.af.mil as I no longer subscribe to the
>mathgroup.
>

```

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