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# slasy2

```
NAME
SLASY2 - solve for the N1 by N2 matrix X, 1 <= N1,N2 <= 2,
in   op(TL)*X + ISGN*X*op(TR) = SCALE*B,

SYNOPSIS
SUBROUTINE SLASY2( 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

REAL           SCALE, XNORM

REAL           B( LDB, * ), TL( LDTL, * ), TR( LDTR, *
), X( LDX, * )

PURPOSE
SLASY2 solves for the N1 by N2 matrix X, 1 <= N1,N2 <= 2, in

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 tran-
spose 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) REAL 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) REAL 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) REAL 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) REAL
On exit, SCALE contains the scale factor. SCALE is
chosen less than or equal to 1 to prevent the solu-
tion overflowing.

X       (output) REAL 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) REAL
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 perturbed to get a nonsingular equation.  NOTE:
In the interests of speed, this routine does not
check the inputs for errors.
```