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
slagv2 dlagv2
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.