zlaesy (l) - Linux Manuals
zlaesy: computes the eigendecomposition of a 2-by-2 symmetric matrix ( ( A, B );( B, C ) ) provided the norm of the matrix of eigenvectors is larger than some threshold value
NAME
ZLAESY - computes the eigendecomposition of a 2-by-2 symmetric matrix ( ( A, B );( B, C ) ) provided the norm of the matrix of eigenvectors is larger than some threshold valueSYNOPSIS
- SUBROUTINE ZLAESY(
- A, B, C, RT1, RT2, EVSCAL, CS1, SN1 )
- COMPLEX*16 A, B, C, CS1, EVSCAL, RT1, RT2, SN1
PURPOSE
ZLAESY computes the eigendecomposition of a 2-by-2 symmetric matrix(
ARGUMENTS
- A (input) COMPLEX*16
- The ( 1, 1 ) element of input matrix.
- B (input) COMPLEX*16
- The ( 1, 2 ) element of input matrix. The ( 2, 1 ) element is also given by B, since the 2-by-2 matrix is symmetric.
- C (input) COMPLEX*16
- The ( 2, 2 ) element of input matrix.
- RT1 (output) COMPLEX*16
- The eigenvalue of larger modulus.
- RT2 (output) COMPLEX*16
- The eigenvalue of smaller modulus.
- EVSCAL (output) COMPLEX*16
- The complex value by which the eigenvector matrix was scaled to make it orthonormal. If EVSCAL is zero, the eigenvectors were not computed. This means one of two things: the 2-by-2 matrix could not be diagonalized, or the norm of the matrix of eigenvectors before scaling was larger than the threshold value THRESH (set below).
- CS1 (output) COMPLEX*16
-
SN1 (output) COMPLEX*16
If EVSCAL .NE. 0, ( CS1, SN1 ) is the unit right eigenvector
for RT1.