Re: Algebra on complex expressions: Collect

• To: mathgroup at smc.vnet.net
• Subject: [mg15238] Re: Algebra on complex expressions: Collect
• From: Rolf Mertig <rolf at mertig.com>
• Date: Sun, 27 Dec 1998 03:58:30 -0500
• Organization: Mertig Research & Consulting
• References: <75q17d\$229@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Ross, Sean wrote:
>
> 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.
You can read mathgroup through www.dejanews.com without subscribing,
right?

In[1]:=
cc[z_,r___]:=Collect[z/.Complex[w_,v_]:>comp[w,v],comp[__],r]/.comp->Complex

In[2]:= cc[ (a+b I) c + (d+e I) x]

Out[2]= a c + d x + I (b c + e x)

--

Dr. Rolf Mertig
Mertig Research & Consulting
Mathematica training and programming Development and distribution of
FeynCalc  Amsterdam, The Netherlands http://www.mertig.com

```

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