SRC/strsyl.f(3)

NAME
SRC/strsyl.f

SYNOPSIS

  Functions/Subroutines
subroutine strsyl (trana, tranb, isgn, m, n, a, lda, b, ldb, c, ldc, scale, info)
STRSYL

Function/Subroutine Documentation

  subroutine strsyl (character trana, character tranb, integer isgn, integer m, integer n, real, dimension( lda, * ) a, integer lda, real, dimension( ldb, * ) b, integer ldb, real, dimension( ldc, * ) c, integer ldc, real scale, integer info)

STRSYL

Purpose:

     STRSYL 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 SHSEQR), 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 REAL 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 REAL 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 REAL 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 REAL
              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.

Definition at line 162 of file strsyl.f.

Author

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