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

**References**:**Replacement gyrations***From:*carlos@colorado.edu