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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.