Fortran 90: DSYEV and associating eigenvalues and eigenvectors

3
votes

I am very new to programming and fortran in particular. I am using the LAPACK (Linear Algebra Package) software package for Fortran to find the eigenvalues and eigenvectors of a large symmetrical real matrix. Specifically, I calculate a scalar from each eigenvector, and I want to graph it against its associated eigenvalue.

I am using the subroutine DSYEV of LAPACK to do this. However, DSYEV outputs the eigenvalues in ascending order, and I'm not sure how it orders the eigenvectors. Is there a way to associate each eigenvector with its eigenvalue?

Edit: The official page for DSYEV is here: http://www.netlib.org/lapack/double/dsyev.f Here is another page about it: http://www.nag.co.uk/numeric/fl/nagd...F08/f08faf.xml

1
matrixfortranfortran90lapackeigenvector
stackoverflow.com/questions/7601077/… – ev-br

1 Answers

3
votes

They should be in the same order. You can actually check this by matrix multiplication. It is much easier and faster, than finding the eigenvectors.