Visible to Intel only — GUID: GUID-12A9967A-5C96-4A97-AF4A-33F0A50C382E
Visible to Intel only — GUID: GUID-12A9967A-5C96-4A97-AF4A-33F0A50C382E
?lasy2
Solves the Sylvester matrix equation where the matrices are of order 1 or 2.
Syntax
call slasy2( ltranl, ltranr, isgn, n1, n2, tl, ldtl, tr, ldtr, b, ldb, scale, x, ldx, xnorm, info )
call dlasy2( ltranl, ltranr, isgn, n1, n2, tl, ldtl, tr, ldtr, b, ldb, scale, x, ldx, xnorm, info )
Include Files
- mkl.fi
Description
The routine solves for the n1-by-n2 matrix X, 1 ≤ n1, n2 ≤ 2, in
op(TL)*X + isgn*X*op(TR) = scale*B,
where
TL is n1-by-n1,
TR is n2-by-n2,
B is n1-by-n2,
and isgn = 1 or -1. op(T) = T or TT, where TT denotes the transpose of T.
Input Parameters
- ltranl
-
LOGICAL.
On entry, ltranl specifies the op(TL):
= .FALSE., op(TL) = TL,
= .TRUE., op(TL) = (TL)T.
- ltranr
-
LOGICAL.
On entry, ltranr specifies the op(TR):
= .FALSE., op(TR) = TR,
= .TRUE., op(TR) = (TR)T.
- isgn
-
INTEGER. On entry, isgn specifies the sign of the equation as described before. isgn may only be 1 or -1.
- n1
-
INTEGER. On entry, n1 specifies the order of matrix TL.
n1 may only be 0, 1 or 2.
- n2
-
INTEGER. On entry, n2 specifies the order of matrix TR.
n2 may only be 0, 1 or 2.
- tl
-
REAL for slasy2
DOUBLE PRECISION for dlasy2.
Array, DIMENSION (ldtl,2).
On entry, tl contains an n1-by-n1 matrix TL.
- ldtl
-
INTEGER.The leading dimension of the matrix TL.
ldtl≥ max(1,n1).
- tr
-
REAL for slasy2
DOUBLE PRECISION for dlasy2.
Array, DIMENSION (ldtr,2). On entry, tr contains an n2-by-n2 matrix TR.
- ldtr
-
INTEGER. The leading dimension of the matrix TR.
ldtr≥ max(1,n2).
- b
-
REAL for slasy2
DOUBLE PRECISION for dlasy2.
Array, DIMENSION (ldb,2). On entry, the n1-by-n2 matrix B contains the right-hand side of the equation.
- ldb
-
INTEGER. The leading dimension of the matrix B.
ldb≥ max(1,n1).
- ldx
-
INTEGER. The leading dimension of the output matrix X.
ldx≥ max(1,n1).
Output Parameters
- scale
-
REAL for slasy2
DOUBLE PRECISION for dlasy2.
On exit, scale contains the scale factor.
scale is chosen less than or equal to 1 to prevent the solution overflowing.
- x
-
REAL for slasy2
DOUBLE PRECISION for dlasy2.
Array, DIMENSION (ldx,2). On exit, x contains the n1-by-n2 solution.
- xnorm
-
REAL for slasy2
DOUBLE PRECISION for dlasy2.
On exit, xnorm is the infinity-norm of the solution.
- info
-
INTEGER. On exit, info is set to 0: successful exit. 1: TL and TR have too close eigenvalues, so TL or TR is perturbed to get a nonsingular equation.
For higher speed, this routine does not check the inputs for errors.