TESTING/LIN/stbt06.f(3)

NAME
TESTING/LIN/stbt06.f

SYNOPSIS

  Functions/Subroutines
subroutine stbt06 (rcond, rcondc, uplo, diag, n, kd, ab, ldab, work, rat)
STBT06

Function/Subroutine Documentation

  subroutine stbt06 (real rcond, real rcondc, character uplo, character diag, integer n, integer kd, real, dimension( ldab, * ) ab, integer ldab, real, dimension( * ) work, real rat)

STBT06

Purpose:

    !>
    !> STBT06 computes a test ratio comparing RCOND (the reciprocal
    !> condition number of a triangular matrix A) and RCONDC, the estimate
    !> computed by STBCON.  Information about the triangular matrix A is
    !> used if one estimate is zero and the other is non-zero to decide if
    !> underflow in the estimate is justified.
    !>

Parameters
    RCOND

    !>          RCOND is REAL
    !>          The estimate of the reciprocal condition number obtained by
    !>          forming the explicit inverse of the matrix A and computing
    !>          RCOND = 1/( norm(A) * norm(inv(A)) ).
    !>

    RCONDC

    !>          RCONDC is REAL
    !>          The estimate of the reciprocal condition number computed by
    !>          STBCON.
    !>

    UPLO

    !>          UPLO is CHARACTER
    !>          Specifies whether the matrix A is upper or lower triangular.
    !>          = 'U':  Upper triangular
    !>          = 'L':  Lower triangular
    !>

    DIAG

    !>          DIAG is CHARACTER
    !>          Specifies whether or not the matrix A is unit triangular.
    !>          = 'N':  Non-unit triangular
    !>          = 'U':  Unit triangular
    !>

    N

    !>          N is INTEGER
    !>          The order of the matrix A.  N >= 0.
    !>

    KD

    !>          KD is INTEGER
    !>          The number of superdiagonals or subdiagonals of the
    !>          triangular band matrix A.  KD >= 0.
    !>

    AB

    !>          AB is REAL array, dimension (LDAB,N)
    !>          The upper or lower triangular band matrix A, stored in the
    !>          first kd+1 rows of the array. The j-th column of A is stored
    !>          in the j-th column of the array AB as follows:
    !>          if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j;
    !>          if UPLO = 'L', AB(1+i-j,j)    = A(i,j) for j<=i<=min(n,j+kd).
    !>

    LDAB

    !>          LDAB is INTEGER
    !>          The leading dimension of the array AB.  LDAB >= KD+1.
    !>

    WORK

    !>          WORK is REAL array, dimension (N)
    !>

    RAT

    !>          RAT is REAL
    !>          The test ratio.  If both RCOND and RCONDC are nonzero,
    !>             RAT = MAX( RCOND, RCONDC )/MIN( RCOND, RCONDC ) - 1.
    !>          If RAT = 0, the two estimates are exactly the same.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 123 of file stbt06.f.

Author

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