MathGroup Archive 2001

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restrictions on parameters

  • To: mathgroup at
  • Subject: [mg31955] restrictions on parameters
  • From: steger at (Thomas Steger)
  • Date: Fri, 14 Dec 2001 04:21:18 -0500 (EST)
  • Sender: owner-wri-mathgroup at

Example: Given the restrictions on the parameters as shown below, I
would like to check the sign of the determinant or the eigenvalues of
Matrix A. The problem seems to be that the restricions on the parameters
are not properly specified.

Clear[a, b, c, d]
a < 0; b > 0; c > 0; d > 0;
A = {{a, b}, {c, d}};

eigen = Eigensystem[A];
{d1, d2} = {eigen[[1, 1]], eigen[[1, 2]]};

det1 = Det[A]
-b c + a d

TrueQ[det1 < 0]

This should be true!

TrueQ[d1 < 0]

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