Fortran LAPACK subroutine DSYEV: order of eigenvalues.

C.L. · 11-07-2011, 09:27 AM

Greetings. The LAPACK software package for fortran is a linear algebra package, and it has a particular subroutine called DSYEV that computes all the eigenvalues and eigenvectors of a real symmetric matrix.
Now, I am calculating a scalar for each eigenvector. I think DSYEV prints out the eigenvalues in ascending order, correct? So how can I associate each scalar with its corresponding eigenvector, or equivalently how can I associate each eigenvector with its eigenvalue?

PTrenholme · 11-09-2011, 10:52 AM

Assuming you're using right eigenvectors, for the matrix M and eigenvector v, M v = c v, where c is the eigenvalue, so c = (M v)i / vi for any non-zero vi.