DLASY2(3)      LAPACK routine of NEC Numeric Library Collection      DLASY2(3)



NAME
       DLASY2

SYNOPSIS
       SUBROUTINE DLASY2 (LTRANL, LTRANR, ISGN, N1, N2, TL, LDTL, TR, LDTR, B,
           LDB, SCALE, X, LDX, XNORM, INFO)



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**T, where T**T denotes the transpose of T.




ARGUMENTS
           LTRANL    (input)
                     LTRANL is LOGICAL
                     On entry, LTRANL specifies the op(TL):
                        = .FALSE., op(TL) = TL,
                        = .TRUE., op(TL) = TL**T.

           LTRANR    (input)
                     LTRANR is LOGICAL
                     On entry, LTRANR specifies the op(TR):
                       = .FALSE., op(TR) = TR,
                       = .TRUE., op(TR) = TR**T.

           ISGN      (input)
                     ISGN is INTEGER
                     On entry, ISGN specifies the sign of the equation
                     as described before. ISGN may only be 1 or -1.

           N1        (input)
                     N1 is INTEGER
                     On entry, N1 specifies the order of matrix TL.
                     N1 may only be 0, 1 or 2.

           N2        (input)
                     N2 is INTEGER
                     On entry, N2 specifies the order of matrix TR.
                     N2 may only be 0, 1 or 2.

           TL        (input)
                     TL is DOUBLE PRECISION array, dimension (LDTL,2)
                     On entry, TL contains an N1 by N1 matrix.

           LDTL      (input)
                     LDTL is INTEGER
                     The leading dimension of the matrix TL. LDTL >= max(1,N1).

           TR        (input)
                     TR is DOUBLE PRECISION array, dimension (LDTR,2)
                     On entry, TR contains an N2 by N2 matrix.

           LDTR      (input)
                     LDTR is INTEGER
                     The leading dimension of the matrix TR. LDTR >= max(1,N2).

           B         (input)
                     B is DOUBLE PRECISION array, dimension (LDB,2)
                     On entry, the N1 by N2 matrix B contains the right-hand
                     side of the equation.

           LDB       (input)
                     LDB is INTEGER
                     The leading dimension of the matrix B. LDB >= max(1,N1).

           SCALE     (output)
                     SCALE is 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)
                     X is DOUBLE PRECISION array, dimension (LDX,2)
                     On exit, X contains the N1 by N2 solution.

           LDX       (input)
                     LDX is INTEGER
                     The leading dimension of the matrix X. LDX >= max(1,N1).

           XNORM     (output)
                     XNORM is DOUBLE PRECISION
                     On exit, XNORM is the infinity-norm of the solution.

           INFO      (output)
                     INFO is 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.



LAPACK routine                  31 October 2017                      DLASY2(3)