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Replacement gyrations

  • To: mathgroup at
  • Subject: [mg55872] Replacement gyrations
  • From: carlos at
  • Date: Fri, 8 Apr 2005 01:37:00 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

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
            (-(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?

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