SRC/strsyl3.f(3)

NAME
SRC/strsyl3.f

SYNOPSIS

  Functions/Subroutines
subroutine strsyl3 (trana, tranb, isgn, m, n, a, lda, b, ldb, c, ldc, scale, iwork, liwork, swork, ldswork, info)
STRSYL3

Function/Subroutine Documentation

  subroutine strsyl3 (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, dimension( * ) iwork, integer liwork, real, dimension( ldswork, * ) swork, integer ldswork, integer info)

STRSYL3

Purpose:

    !>
    !>  STRSYL3 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.
    !>
    !>  This is the block version of the algorithm.
    !>

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.
    !>

    IWORK

    !>          IWORK is INTEGER array, dimension (MAX(1,LIWORK))
    !>          On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.
    !>

    LIWORK

    !>          IWORK is INTEGER
    !>          The dimension of the array IWORK. LIWORK >=  ((M + NB - 1) / NB + 1)
    !>          + ((N + NB - 1) / NB + 1), where NB is the optimal block size.
    !>
    !>          If LIWORK = -1, then a workspace query is assumed; the routine
    !>          only calculates the optimal dimension of the IWORK array,
    !>          returns this value as the first entry of the IWORK array, and
    !>          no error message related to LIWORK is issued by XERBLA.
    !>

    SWORK

    !>          SWORK is REAL array, dimension (MAX(2, ROWS),
    !>          MAX(1,COLS)).
    !>          On exit, if INFO = 0, SWORK(1) returns the optimal value ROWS
    !>          and SWORK(2) returns the optimal COLS.
    !>

    LDSWORK

    !>          LDSWORK is INTEGER
    !>          LDSWORK >= MAX(2,ROWS), where ROWS = ((M + NB - 1) / NB + 1)
    !>          and NB is the optimal block size.
    !>
    !>          If LDSWORK = -1, then a workspace query is assumed; the routine
    !>          only calculates the optimal dimensions of the SWORK matrix,
    !>          returns these values as the first and second entry of the SWORK
    !>          matrix, and no error message related LWORK is issued by XERBLA.
    !>

    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).
    !>

Definition at line 196 of file strsyl3.f.

Author

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