Compute the eigenvalues of a real symmetric matrix.
call EigValSym (ain
, n
, eval
, ul
)
ain
: input, real(dp), dimension (n
, n
)
: The input real symmetric matrix. By default, only the upper portion of the matrix is used.
n
: input, integer
: The rank of the matrix ain
.
eval
: output, real(dp), dimension (n
)
: The eigenvalues of ain
, sorted from largest to smallest.
ul
: optional, input, character, default = U
: If U
then the upper portion of the matrix ain
will be used (default). If L
then the lower portion of the matrix ain
will be used.
EigValSym
will calculate the eigenvalues of a real symmetric matrix. By default, only the upper portion of the matrix is used, but this can be changed by the optional argument ul
. The eigenvalues are sorted from largest to smallest. The matrix ain
is first factorized into a tridiagonal matrix using the LAPACK routine DSYTRD
, and then the eigenvalues are calculated by a call to DSTEGR
.