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MathGroup Archive 2000

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imposing side conditions on Solve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24029] imposing side conditions on Solve
  • From: Albert Maydeu-Olivares <amaydeu at tinet.fut.es>
  • Date: Tue, 20 Jun 2000 03:07:41 -0400 (EDT)
  • Organization: University of Barcelona
  • Sender: owner-wri-mathgroup at wolfram.com

Hello everyone,

I have two questions for the group on using Solve.

1) How do I impose conditions on the solution? Consider the following
example


omega1 = {l1^2 + ps1, l1*l2, l2^2 + ps2, l1*l3, l2*l3, l3^2 + ps3,
l1*l4, l2*l4, l3*l4, 
    l4^2 + ps4}; 
theta1 = {l1, l2, l3, l4, ps1, ps2, ps3, ps4}; 
omega2 = {e1^2*(ll1^2 + pp1), e1*e2*ll1*ll2, e2^2*(ll2^2 + pp2),
e1*e3*ll1*ll3, e2*e3*ll2*ll3, 
    e3^2*(ll3^2 + pp3), e1*e4*ll1*ll4, e2*e4*ll2*ll4, e3*e4*ll3*ll4,
e4^2*(ll4^2 + pp4)}; 
theta2 = {ll1, ll2, ll3, ll4, pp1, pp2, pp3, pp4}; 

sol = Solve[omega1 == omega2, theta1]

omega2 ==Simplify[omega1/.Flatten[sol[[1]]]]

So it works. However, how do I impose the condition that all elements of
theta1 must be positive?

2) Why Solve fails to say that there is no solution to this problem?

omega1={1 + ps1, 1, 1 + ps2, 1, 1, 1 + ps3, 1, 1, 1, 1 + ps4};
theta1={ps1, ps2, ps3, ps4};
omega2={e1^2*(1 + pp1), e1*e2, e2^2*(1 + pp2), e1*e3, e2*e3, e3^2*(1 +
pp3), e1*e4, e2*e4, e3*e4, 
  e4^2*(1 + pp4)};
theta2={pp1, pp2, pp3, pp4};
sol = Solve[omega1 == omega2, theta1]

omega2 == Simplify[omega1/.sol[[1]]]

Thank you for your help,

Albert


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