SLASY2 (3lapack)

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 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.