Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
?lanv2
Computes the Schur factorization of a real 2-by-2 nonsymmetric matrix in standard form.
Syntax
call slanv2 ( a , b , c , d , rt1r , rt1i , rt2r , rt2i , cs , sn )
call dlanv2 ( a , b , c , d , rt1r , rt1i , rt2r , rt2i , cs , sn )
Include Files
mkl.fi
Description
slanv2 dlanv2
The routine computes the Schur factorization of a real 2-by-2 nonsymmetric matrix in standard form:
where either
cc = 0 so that aa and dd are real eigenvalues of the matrix, or
aa = dd and bb*cc < 0 , so that aa± sqrt(bb*cc) are complex conjugate eigenvalues.
The routine was adjusted to reduce the risk of cancellation errors, when computing real eigenvalues, and to ensure, if possible, that abs(rt1r) ≥ abs(rt2r) .
Input Parameters
- a , b , c , d
-
REAL for slanv2 DOUBLE PRECISION for dlanv2 . On entry, elements of the input matrix.
Output Parameters
- a , b , c , d
-
On exit, overwritten by the elements of the standardized Schur form.
- rt1r , rt1i , rt2r , rt2i
-
REAL for slanv2 DOUBLE PRECISION for dlanv2 . The real and imaginary parts of the eigenvalues. If the eigenvalues are a complex conjugate pair, rt1i > 0 .
- cs , sn
-
REAL for slanv2 DOUBLE PRECISION for dlanv2 . Parameters of the rotation matrix.