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 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) 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 solution 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.