NAME

       dtrsyl.f -

SYNOPSIS

   Functions/Subroutines
       subroutine dtrsyl (TRANA, TRANB, ISGN, M, N, A, LDA, B, LDB, C, LDC, SCALE, INFO)
           DTRSYL

Function/Subroutine Documentation

   subroutine dtrsyl (characterTRANA, characterTRANB, integerISGN, integerM, integerN, double
       precision, dimension( lda, * )A, integerLDA, double precision, dimension( ldb, * )B,
       integerLDB, double precision, dimension( ldc, * )C, integerLDC, double precisionSCALE,
       integerINFO)
       DTRSYL

       Purpose:

            DTRSYL solves the real Sylvester matrix equation:

               op(A)*X + X*op(B) = scale*C or
               op(A)*X - X*op(B) = scale*C,

            where op(A) = A or A**T, and  A and B are both upper quasi-
            triangular. A is M-by-M and B is N-by-N; the right hand side C and
            the solution X are M-by-N; and scale is an output scale factor, set
            <= 1 to avoid overflow in X.

            A and B must be in Schur canonical form (as returned by DHSEQR), that
            is, block upper triangular with 1-by-1 and 2-by-2 diagonal blocks;
            each 2-by-2 diagonal block has its diagonal elements equal and its
            off-diagonal elements of opposite sign.

       Parameters:
           TRANA

                     TRANA is CHARACTER*1
                     Specifies the option op(A):
                     = 'N': op(A) = A    (No transpose)
                     = 'T': op(A) = A**T (Transpose)
                     = 'C': op(A) = A**H (Conjugate transpose = Transpose)

           TRANB

                     TRANB is CHARACTER*1
                     Specifies the option op(B):
                     = 'N': op(B) = B    (No transpose)
                     = 'T': op(B) = B**T (Transpose)
                     = 'C': op(B) = B**H (Conjugate transpose = Transpose)

           ISGN

                     ISGN is INTEGER
                     Specifies the sign in the equation:
                     = +1: solve op(A)*X + X*op(B) = scale*C
                     = -1: solve op(A)*X - X*op(B) = scale*C

           M

                     M is INTEGER
                     The order of the matrix A, and the number of rows in the
                     matrices X and C. M >= 0.

           N

                     N is INTEGER
                     The order of the matrix B, and the number of columns in the
                     matrices X and C. N >= 0.

           A

                     A is DOUBLE PRECISION array, dimension (LDA,M)
                     The upper quasi-triangular matrix A, in Schur canonical form.

           LDA

                     LDA is INTEGER
                     The leading dimension of the array A. LDA >= max(1,M).

           B

                     B is DOUBLE PRECISION array, dimension (LDB,N)
                     The upper quasi-triangular matrix B, in Schur canonical form.

           LDB

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

           C

                     C is DOUBLE PRECISION array, dimension (LDC,N)
                     On entry, the M-by-N right hand side matrix C.
                     On exit, C is overwritten by the solution matrix X.

           LDC

                     LDC is INTEGER
                     The leading dimension of the array C. LDC >= max(1,M)

           SCALE

                     SCALE is DOUBLE PRECISION
                     The scale factor, scale, set <= 1 to avoid overflow in X.

           INFO

                     INFO is INTEGER
                     = 0: successful exit
                     < 0: if INFO = -i, the i-th argument had an illegal value
                     = 1: A and B have common or very close eigenvalues; perturbed
                          values were used to solve the equation (but the matrices
                          A and B are unchanged).

       Author:
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Date:
           November 2011

       Definition at line 164 of file dtrsyl.f.

Author

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