TESTING/EIG/ssvdch.f(3)

NAME
TESTING/EIG/ssvdch.f

SYNOPSIS

  Functions/Subroutines
subroutine ssvdch (n, s, e, svd, tol, info)
SSVDCH

Function/Subroutine Documentation

  subroutine ssvdch (integer n, real, dimension( * ) s, real, dimension( * ) e, real, dimension( * ) svd, real tol, integer info)

SSVDCH

Purpose:

     SSVDCH 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
     SSVDCT). Here EPS=TOL*MAX(N/10,1)*MACHEP, 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 REAL array, dimension (N)
              The diagonal entries of the bidiagonal matrix B.

    E

              E is REAL array, dimension (N-1)
              The superdiagonal entries of the bidiagonal matrix B.

    SVD

              SVD is REAL array, dimension (N)
              The computed singular values to be checked.

    TOL

              TOL is REAL
              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*MACHEPS)
              >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 ssvdch.f.

Author

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