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EigValSym
Compute the eigenvalues of a real symmetric matrix.
Usage
call EigValSym (ain
, n
, eval
, ul
)
Parameters
ain
: input, real*8, 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*8, 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 matrixain
will be used (default). IfL
then the lower portion of the matrixain
will be used.
Description
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
.
See also
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