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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