TESTING/EIG/dsvdch.f(3)

NAME
TESTING/EIG/dsvdch.f

SYNOPSIS

  Functions/Subroutines
subroutine dsvdch (n, s, e, svd, tol, info)
DSVDCH

Function/Subroutine Documentation

  subroutine dsvdch (integer n, double precision, dimension( * ) s, double precision, dimension( * ) e, double precision, dimension( * ) svd, double precision tol, integer info)

DSVDCH

Purpose:

    !>
    !> DSVDCH checks to see if SVD(1) ,..., SVD(N) are accurate singular
    !> values of the bidiagonal matrix B with diagonal entries
    !> S(1) ,..., S(N) and superdiagonal entries E(1) ,..., E(N-1)).
    !> It does this by expanding each SVD(I) into an interval
    !> [SVD(I) * (1-EPS) , SVD(I) * (1+EPS)], merging overlapping intervals
    !> if any, and using Sturm sequences to count and verify whether each
    !> resulting interval has the correct number of singular values (using
    !> DSVDCT). Here EPS=TOL*MAX(N/10,1)*MAZHEP, where MACHEP is the
    !> machine precision. The routine assumes the singular values are sorted
    !> with SVD(1) the largest and SVD(N) smallest.  If each interval
    !> contains the correct number of singular values, INFO = 0 is returned,
    !> otherwise INFO is the index of the first singular value in the first
    !> bad interval.
    !>

Parameters
    N

    !>          N is INTEGER
    !>          The dimension of the bidiagonal matrix B.
    !>

    S

    !>          S is DOUBLE PRECISION array, dimension (N)
    !>          The diagonal entries of the bidiagonal matrix B.
    !>

    E

    !>          E is DOUBLE PRECISION array, dimension (N-1)
    !>          The superdiagonal entries of the bidiagonal matrix B.
    !>

    SVD

    !>          SVD is DOUBLE PRECISION array, dimension (N)
    !>          The computed singular values to be checked.
    !>

    TOL

    !>          TOL is DOUBLE PRECISION
    !>          Error tolerance for checking, a multiplier of the
    !>          machine precision.
    !>

    INFO

    !>          INFO is INTEGER
    !>          =0 if the singular values are all correct (to within
    !>             1 +- TOL*MAZHEPS)
    !>          >0 if the interval containing the INFO-th singular value
    !>             contains the incorrect number of singular values.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 96 of file dsvdch.f.

Author

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