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MathGroup Archive 2007

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Solve[] and Eliminate[] choke on simple systems of equations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg74719] Solve[] and Eliminate[] choke on simple systems of equations
  • From: darrell.long at gmail.com
  • Date: Mon, 2 Apr 2007 06:54:26 -0400 (EDT)

Hi,

I am trying to convert some of my old stuff from another system to Mathematica.
Below is an example of a Markov model that takes the other system a couple of
seconds to solve, but Mathematica chews on forever (I gave up after
about 30 minutes).

Since I'm a Mathematica newbie, perhaps there is some limitation I am
not aware of?

eqns = {3*L*P333 == U*(P323 + P322 + P223 + P221 + P120),
(K + 2*L + U)*P323 == 3*L*P333,
(K + 2*U + L)*P313 == 2*L*P323,
(2*L + U)*P322 == 2*U*P312,
(2*U + L)*P312 == 2*L*P322 + 3*U*P302,
3*U*P302 == L*P312 + L*P313,
(2*L + U)*P223 == U*(2*P213 + P212) + 2*U*P313 + U*(2*P113 + P111) +
K*P323,
(K + 2*U + L)*P213 == 2*L*P223,
(2*U + L)*P212 == L*P221 + 2*U*P202,
3*U*P202 == L*(P213 + P212 + P211),
(2*L + U)*P221 == U*(P212 + 2*P211),
(2*U + L)*P211 == L*P221 + U*P202
(L + 2*U)*P113 == K*P313 + K*P213 + U*P102,
3*U*P102 == L*P113 + L*P111,
(2*U + L)*P111 == 2*U*P102 + 2*L*P120,
(2*L + U)*P120 == U*P111,
P333 + P323 + P313 + P322 +
        P312 + P302 + P223 + P213 + P212 + P202 + P221 + P211 + P113 +
P102 +
        P111 + P120 == 1}
vars = {P333, P323, P313, P322, P312, P302, P223, P213, P212, P202,
P221,
    P211, P113, P102, P111, P120}

A = Solve[eqns, vars]



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