subroutine dlasy2 (LTRANL, LTRANR, ISGN, N1, N2, TL, LDTL, TR, LDTR, B, LDB, SCALE, X, LDX, XNORM, INFO)
DLASY2 solves the Sylvester matrix equation where the matrices are of order 1 or 2.
DLASY2 solves the Sylvester matrix equation where the matrices are of order 1 or 2.
Purpose:
DLASY2 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 T**T, where T**T denotes the transpose of T.
Parameters:
LTRANL is LOGICAL On entry, LTRANL specifies the op(TL): = .FALSE., op(TL) = TL, = .TRUE., op(TL) = TL**T.
LTRANR
LTRANR is LOGICAL On entry, LTRANR specifies the op(TR): = .FALSE., op(TR) = TR, = .TRUE., op(TR) = TR**T.
ISGN
ISGN is INTEGER On entry, ISGN specifies the sign of the equation as described before. ISGN may only be 1 or -1.
N1
N1 is INTEGER On entry, N1 specifies the order of matrix TL. N1 may only be 0, 1 or 2.
N2
N2 is INTEGER On entry, N2 specifies the order of matrix TR. N2 may only be 0, 1 or 2.
TL
TL is DOUBLE PRECISION array, dimension (LDTL,2) On entry, TL contains an N1 by N1 matrix.
LDTL
LDTL is INTEGER The leading dimension of the matrix TL. LDTL >= max(1,N1).
TR
TR is DOUBLE PRECISION array, dimension (LDTR,2) On entry, TR contains an N2 by N2 matrix.
LDTR
LDTR is INTEGER The leading dimension of the matrix TR. LDTR >= max(1,N2).
B
B is DOUBLE PRECISION array, dimension (LDB,2) On entry, the N1 by N2 matrix B contains the right-hand side of the equation.
LDB
LDB is INTEGER The leading dimension of the matrix B. LDB >= max(1,N1).
SCALE
SCALE is DOUBLE PRECISION On exit, SCALE contains the scale factor. SCALE is chosen less than or equal to 1 to prevent the solution overflowing.
X
X is DOUBLE PRECISION array, dimension (LDX,2) On exit, X contains the N1 by N2 solution.
LDX
LDX is INTEGER The leading dimension of the matrix X. LDX >= max(1,N1).
XNORM
XNORM is DOUBLE PRECISION On exit, XNORM is the infinity-norm of the solution.
INFO
INFO is 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. NOTE: In the interests of speed, this routine does not check the inputs for errors.
Author:
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
Definition at line 176 of file dlasy2.f.
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