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MathGroup Archive 1993

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Solve

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: Solve
  • From: vdaele at ieper.lhs.be (Marc Van Daele)
  • Date: Tue, 31 Aug 93 09:52:23 +0200

Hi,

I have two quite simple equations which Mma is not able to solve.
Any ideas why?

1)
Solve[{(mu*S0*X0*(1 - y))/y == a0,
       (mu^2*S0*X0^2*(-1 + y))/y^2 == a1}, {mu, S0}]

takes indefinetely (at least several hours)
(NextStation)


2)
So I need to help Mma like this: 
- first solve S0 from first equation, next replace that solution in second
  equation and solve mu from that equation

sol1s0  = Flatten[Simplify[
		Solve[(mu*S0*X0*(1 - y))/y == a0, S0]]] 
sol1mu  = Flatten[Simplify[
		Solve[(mu^2*S0*X0^2*(-1 + y))/y^2 == a1 /. sol1s0, mu]]]
sol1s0  = Flatten[Simplify[sol1s0 /. sol1mu]]



Which results in
         a1 y
{mu -> -(-----)}
         a0 X0


            2
          a0
{S0 -> ----------}
       -a1 + a1 y

3)
Why is this set of equation so difficult for Mma.
And is there an easier way to solve these equations than holding Mma's hands 
like this.  (I also have a similar problem with six variables)

Thanks for any help,

Marc Van Daele
vdaele at lhs.be







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