DLASY2(l) ) DLASY2(l)NAME
DLASY2 - solve for the N1 by N2 matrix X, 1 <= N1,N2 <= 2, in op(TL)*X
+ ISGN*X*op(TR) = SCALE*B,
SYNOPSIS
SUBROUTINE DLASY2( LTRANL, LTRANR, ISGN, N1, N2, TL, LDTL, TR, LDTR, B,
LDB, SCALE, X, LDX, XNORM, INFO )
LOGICAL LTRANL, LTRANR
INTEGER INFO, ISGN, LDB, LDTL, LDTR, LDX, N1, N2
DOUBLE PRECISION SCALE, XNORM
DOUBLE PRECISION B( LDB, * ), TL( LDTL, * ), TR( LDTR, * ),
X( LDX, * )
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', where T' denotes the
transpose of T.
ARGUMENTS
LTRANL (input) LOGICAL
On entry, LTRANL specifies the op(TL): = .FALSE., op(TL) = TL,
= .TRUE., op(TL) = TL'.
LTRANR (input) LOGICAL
On entry, LTRANR specifies the op(TR): = .FALSE., op(TR) = TR,
= .TRUE., op(TR) = TR'.
ISGN (input) INTEGER
On entry, ISGN specifies the sign of the equation as described
before. ISGN may only be 1 or -1.
N1 (input) INTEGER
On entry, N1 specifies the order of matrix TL. N1 may only be
0, 1 or 2.
N2 (input) INTEGER
On entry, N2 specifies the order of matrix TR. N2 may only be
0, 1 or 2.
TL (input) DOUBLE PRECISION array, dimension (LDTL,2)
On entry, TL contains an N1 by N1 matrix.
LDTL (input) INTEGER
The leading dimension of the matrix TL. LDTL >= max(1,N1).
TR (input) DOUBLE PRECISION array, dimension (LDTR,2)
On entry, TR contains an N2 by N2 matrix.
LDTR (input) INTEGER
The leading dimension of the matrix TR. LDTR >= max(1,N2).
B (input) DOUBLE PRECISION array, dimension (LDB,2)
On entry, the N1 by N2 matrix B contains the right-hand side of
the equation.
LDB (input) INTEGER
The leading dimension of the matrix B. LDB >= max(1,N1).
SCALE (output) DOUBLE PRECISION
On exit, SCALE contains the scale factor. SCALE is chosen less
than or equal to 1 to prevent the solution overflowing.
X (output) DOUBLE PRECISION array, dimension (LDX,2)
On exit, X contains the N1 by N2 solution.
LDX (input) INTEGER
The leading dimension of the matrix X. LDX >= max(1,N1).
XNORM (output) DOUBLE PRECISION
On exit, XNORM is the infinity-norm of the solution.
INFO (output) INTEGER
On exit, INFO is set to 0: successful exit.
1: TL and TR have too close eigenvalues, so TL or TR is per‐
turbed to get a nonsingular equation. NOTE: In the interests
of speed, this routine does not check the inputs for errors.
LAPACK version 3.0 15 June 2000 DLASY2(l)
