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MathGroup Archive 2005

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Re: Replacement gyrations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55892] Re: [mg55872] Replacement gyrations
  • From: DrBob <drbob at bigfoot.com>
  • Date: Sat, 9 Apr 2005 03:55:32 -0400 (EDT)
  • References: <200504080537.BAA25184@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

Wsol /. a_/b_ :> a/Factor@b

{{W11 -> (A2*x21 + A1*x32)/
      (L86^2*((-x32)*y21 +
        x21*y32)), W12 ->
     -((A2*y21 + A1*y32)/
       (L86^2*(x32*y21 -
         x21*y32))),
    W21 -> (A2*x21 + A1*x32)/
      (L75^2*((-x32)*y21 +
        x21*y32)), W22 ->
     -((A2*y21 + A1*y32)/
       (L75^2*(x32*y21 -
         x21*y32)))}}

or just:

Simplify@Wsol

{{W11 -> (A2*x21 + A1*x32)/
      (L86^2*((-x32)*y21 +
        x21*y32)), W12 ->
     -((A2*y21 + A1*y32)/
       (L86^2*(x32*y21 -
         x21*y32))),
    W21 -> (A2*x21 + A1*x32)/
      (L75^2*((-x32)*y21 +
        x21*y32)), W22 ->
     -((A2*y21 + A1*y32)/
       (L75^2*(x32*y21 -
         x21*y32)))}}

Bobby

On Fri, 8 Apr 2005 01:37:00 -0400 (EDT), <carlos at colorado.edu> wrote:

> A Solve for 4 variables W11,W12,W21,W22 produces, after Simplify
>
>  Wsol={{W11 -> (A2*x21 + A1*x32)/(L86^2*(-(x32*y21) + x21*y32)),
>         W12 -> (A2*y21 + A1*y32)/(-(L86^2*x32*y21) + L86^2*x21*y32),
>         W21 -> (A2*x21 + A1*x32)/(L75^2*(-(x32*y21) + x21*y32)),
>         W22 -> (A2*y21 + A1*y32)/(-(L75^2*x32*y21) + L75^2*x21*y32)}}
>
> Question 1: why do L86^2 and L75^2  come out as a factor in two
> expression denominators and not in the others?  Seems a random event.
>
> This uncertainty inhibits the action of further replacement rules such
> as
>             (-(x32*y21) + x21*y32) -> 2*A123
>
> which works on W11 and W21 only.
>
> Question 2: I tried Collect [Wsol,{L86,L75}] to try to force grouping
> of L86^2 and L75^2, but it has no effect.
> Do I need to say Wsol=Wsol*L86^2*L75^2, Simplify, replace and finally
> Wsol=Wsol/L86^2*L75^2 ? Or fool around with Numerator and Denominator?
>
>
>
>



-- 
DrBob at bigfoot.com


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