Matrix must be a positive definite (geometry problem)

Hi, The code i m using is originally for flow past half cylinder. i need to change the geometry so that the semi circle is replaced by half triangle. when i make this change by modifying geometry coordinates i get an error as follows:

Error using ==> chol

Matrix must be positive definite.

Error in ==> ellipt1 at 35

R = chol(A); Y = R'\B; Z = R\Y;

Error in ==> demo2 at 67

      ZN    = ellipt1(p,t,RDZ,[],W);

The part of the code where this 'chol' function is used and the geometry code is shown in the figures below:

Answer 1

[Erik S.]

Hi,

If you are sure the problem is set up correctely you can solve with the general solver:

Z = A\B;

Chol can only be used for special cases when your matrix A has special properties (Symmetric and positive definite). Most matrices are not and than you have to use the \ operator.