       Re: Non trivial substitution in a very long output

• To: mathgroup at smc.vnet.net
• Subject: [mg123164] Re: Non trivial substitution in a very long output
• From: DrMajorBob <btreat1 at austin.rr.com>
• Date: Fri, 25 Nov 2011 04:54:52 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201111241156.GAA28999@smc.vnet.net>

```It seems to work fine in this example:

piece = Abs[b41]^2 + Abs[b51]^2 + Abs[b61]^2 +
Abs[(b61 x1 + b51 x2 + b41 x3)/x4]^2 +
Abs[(b61 x2 + b51 x3 + b41 x4)/x1]^2 +
Abs[(b61 x1 x3 + b51 (x2 x3 - x1 x4) + b41 (x3^2 - x2 x4))/
x4^2]^2 +
Abs[(b61 (x1 x3^2 - x1 x2 x4) +
b51 (x2 x3^2 - x2^2 x4 - x1 x3 x4) +
b41 (x3^3 - 2 x2 x3 x4 + x1 x4^2))/x4^3]^2;
expr = piece + piece^2 - Sin@piece;
expr //. piece -> p

p + p^2 - Sin[p]

Bobby

On Thu, 24 Nov 2011 05:56:33 -0600, Demind <demind at gmail.com> wrote:

> Hello, my name is Marco. I am experiencing an annoying problem using
> Mathematica. I am dealing with a huge expression, some hundreds of
> lines. I can find 3/4 patterns repeating inside it, and I would really
> like to substitute thme with dummy variables, namely D1, D2, D3, D4. I'm
> expecting the readibility of the equation to be improved after this
> process. As it is right now, it's totally unreadable. I went through
> past topics to find solutions to my problem, but unfortunately none of
> the tricks I tried worked (mainly /. and //.).
>
> I give you a sample of what I would like to do, hoping that someone will
> give me some help:
>
> In my equation, Out = ...
> the following pattern is repeated:
>
> Abs[b41]^2 + Abs[b51]^2 + Abs[b61]^2 + Abs[(b61 x1 + b51 x2 + b41
> x3)/x4]^2 + Abs[(b61 x2 + b51 x3 + b41 x4)/x1]^2 + Abs[(b61 x1 x3 + b51
> (x2 x3 - x1 x4) + b41 (x3^2 - x2 x4))/x4^2]^2 + Abs[(b61 (x1 x3^2 - x1
> x2 x4) + b51 (x2 x3^2 - x2^2 x4 - x1 x3 x4) + b41 (x3^3 - 2 x2 x3 x4 +
> x1 x4^2))/x4^3]^2
>
> I'm doing:
>
> Out //. Abs[b41]^2 + Abs[b51]^2 + Abs[b61]^2 + Abs[(b61 x1 + b51 x2 +
> b41 x3)/x4]^2 + Abs[(b61 x2 + b51 x3 + b41 x4)/x1]^2 + Abs[(b61 x1 x3 +
> b51 (x2 x3 - x1 x4) + b41 (x3^2 - x2 x4))/x4^2]^2 + Abs[(b61 (x1 x3^2 -
> x1 x2 x4) + b51 (x2 x3^2 - x2^2 x4 - x1 x3 x4) + b41 (x3^3 - 2 x2 x3 x4
> + x1 x4^2))/x4^3]^2 -> D1
>
> Here the text is attached in "InputForm", where in my notebook I have it
> in "StandardForm" (I use the latter in my notebook, but here I can't
> reproduce it for obvious reasons). I tried to use the command above both
> in StandardForm and in InputForm with no result.
>
> Thank you very much
>
> Marco
>

--
DrMajorBob at yahoo.com

```

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