Developer Reference for Intel® oneAPI Math Kernel Library for Fortran
?lagv2
Computes the Generalized Schur factorization of a real 2-by-2 matrix pencil ( A , B ) where B is upper triangular.
Syntax
call slagv2(a, lda, b, ldb, alphar, alphai, beta, csl, snl, csr, snr)
call dlagv2(a, lda, b, ldb, alphar, alphai, beta, csl, snl, csr, snr)
Include Files
mkl.fi
Description
The routine computes the Generalized Schur factorization of a real 2-by-2 matrix pencil ( A , B ) where B is upper triangular. The routine computes orthogonal (rotation) matrices given by csl , snl and csr , snr such that:
if the pencil ( A , B ) has two real eigenvalues (include 0/0 or 1/0 types), then
if the pencil ( A , B ) has a pair of complex conjugate eigenvalues, then
where b11 ≥ b22 >0.
Input Parameters
- a , b
-
REAL for slagv2 DOUBLE PRECISION for dlagv2 Arrays: a ( lda , 2) contains the 2-by-2 matrix A ; b ( ldb , 2) contains the upper triangular 2-by-2 matrix B .
- lda
-
INTEGER . The leading dimension of the array a ; lda≥ 2 .
- ldb
-
INTEGER . The leading dimension of the array b ; ldb≥ 2 .
Output Parameters
- a
-
On exit, a is overwritten by the “ A -part” of the generalized Schur form.
- b
-
On exit, b is overwritten by the “ B -part” of the generalized Schur form.
- alphar , alphai , beta
-
REAL for slagv2 DOUBLE PRECISION for dlagv2 . Arrays, dimension (2) each. (alphar(k) + i*alphai(k))/beta(k) are the eigenvalues of the pencil ( A , B ), k=1,2 and i = sqrt(-1) . Note that beta (k) may be zero.
- csl , snl
-
REAL for slagv2 DOUBLE PRECISION for dlagv2 The cosine and sine of the left rotation matrix, respectively.
- csr , snr
-
REAL for slagv2 DOUBLE PRECISION for dlagv2 The cosine and sine of the right rotation matrix, respectively.