NAME

       slasy2.f -

SYNOPSIS

   Functions/Subroutines
       subroutine slasy2 (LTRANL, LTRANR, ISGN, N1, N2, TL, LDTL, TR, LDTR, B, LDB, SCALE, X,
           LDX, XNORM, INFO)
           SLASY2 solves the Sylvester matrix equation where the matrices are of order 1 or 2.

Function/Subroutine Documentation

   subroutine slasy2 (logicalLTRANL, logicalLTRANR, integerISGN, integerN1, integerN2, real,
       dimension( ldtl, * )TL, integerLDTL, real, dimension( ldtr, * )TR, integerLDTR, real,
       dimension( ldb, * )B, integerLDB, realSCALE, real, dimension( ldx, * )X, integerLDX,
       realXNORM, integerINFO)
       SLASY2 solves the Sylvester matrix equation where the matrices are of order 1 or 2.

       Purpose:

            SLASY2 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.

       Parameters:
           LTRANL

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

           LTRANR

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

           ISGN

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

           N1

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

           N2

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

           TL

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

           LDTL

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

           TR

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

           LDTR

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

           B

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

           LDB

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

           SCALE

                     SCALE is REAL
                     On exit, SCALE contains the scale factor. SCALE is chosen
                     less than or equal to 1 to prevent the solution overflowing.

           X

                     X is REAL array, dimension (LDX,2)
                     On exit, X contains the N1 by N2 solution.

           LDX

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

           XNORM

                     XNORM is REAL
                     On exit, XNORM is the infinity-norm of the solution.

           INFO

                     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.

       Author:
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Date:
           September 2012

       Definition at line 174 of file slasy2.f.

Author

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