Visible to Intel only — GUID: GUID-44C585A1-840A-43F4-9A8A-C5D7297AD897
Visible to Intel only — GUID: GUID-44C585A1-840A-43F4-9A8A-C5D7297AD897
?laesy
Computes the eigenvalues and eigenvectors of a 2-by-2 complex symmetric matrix, and checks that the norm of the matrix of eigenvectors is larger than a threshold value.
Syntax
call claesy( a, b, c, rt1, rt2, evscal, cs1, sn1 )
call zlaesy( a, b, c, rt1, rt2, evscal, cs1, sn1 )
Include Files
- mkl.fi
Description
The routine performs the eigendecomposition of a 2-by-2 symmetric matrix
provided the norm of the matrix of eigenvectors is larger than some threshold value.
rt1 is the eigenvalue of larger absolute value, and rt2 of smaller absolute value. If the eigenvectors are computed, then on return (cs1, sn1) is the unit eigenvector for rt1, hence
Input Parameters
- a, b, c
-
COMPLEX for claesy
DOUBLE COMPLEX for zlaesy
Elements of the input matrix.
Output Parameters
- rt1, rt2
-
COMPLEX for claesy
DOUBLE COMPLEX for zlaesy
Eigenvalues of larger and smaller modulus, respectively.
- evscal
-
COMPLEX for claesy
DOUBLE COMPLEX for zlaesy
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 to 0.1E0).
- cs1, sn1
-
COMPLEX for claesy
DOUBLE COMPLEX for zlaesy
If evscal is not zero, then (cs1, sn1) is the unit right eigenvector for rt1.