dlasy2 (3)  Linux Manuals
NAME
dlasy2.f 
SYNOPSIS
Functions/Subroutines
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.
Function/Subroutine Documentation
subroutine dlasy2 (logicalLTRANL, logicalLTRANR, integerISGN, integerN1, integerN2, double precision, dimension( ldtl, * )TL, integerLDTL, double precision, dimension( ldtr, * )TR, integerLDTR, double precision, dimension( ldb, * )B, integerLDB, double precisionSCALE, double precision, dimension( ldx, * )X, integerLDX, double precisionXNORM, integerINFO)
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
LTRANL is LOGICAL On entry, LTRANL specifies the op(TL): = .FALSE., op(TL) = TL, = .TRUE., op(TL) = TL**T.
LTRANRLTRANR is LOGICAL On entry, LTRANR specifies the op(TR): = .FALSE., op(TR) = TR, = .TRUE., op(TR) = TR**T.
ISGNISGN is INTEGER On entry, ISGN specifies the sign of the equation as described before. ISGN may only be 1 or 1.
N1N1 is INTEGER On entry, N1 specifies the order of matrix TL. N1 may only be 0, 1 or 2.
N2N2 is INTEGER On entry, N2 specifies the order of matrix TR. N2 may only be 0, 1 or 2.
TLTL is DOUBLE PRECISION array, dimension (LDTL,2) On entry, TL contains an N1 by N1 matrix.
LDTLLDTL is INTEGER The leading dimension of the matrix TL. LDTL >= max(1,N1).
TRTR is DOUBLE PRECISION array, dimension (LDTR,2) On entry, TR contains an N2 by N2 matrix.
LDTRLDTR is INTEGER The leading dimension of the matrix TR. LDTR >= max(1,N2).
BB is DOUBLE PRECISION array, dimension (LDB,2) On entry, the N1 by N2 matrix B contains the righthand side of the equation.
LDBLDB is INTEGER The leading dimension of the matrix B. LDB >= max(1,N1).
SCALESCALE is DOUBLE PRECISION On exit, SCALE contains the scale factor. SCALE is chosen less than or equal to 1 to prevent the solution overflowing.
XX is DOUBLE PRECISION array, dimension (LDX,2) On exit, X contains the N1 by N2 solution.
LDXLDX is INTEGER The leading dimension of the matrix X. LDX >= max(1,N1).
XNORMXNORM is DOUBLE PRECISION On exit, XNORM is the infinitynorm of the solution.
INFOINFO 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 Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
 September 2012
Definition at line 174 of file dlasy2.f.
Author
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