TESTING/EIG/dstech.f(3)

NAME
TESTING/EIG/dstech.f

SYNOPSIS

  Functions/Subroutines
subroutine dstech (n, a, b, eig, tol, work, info)
DSTECH

Function/Subroutine Documentation

  subroutine dstech (integer n, double precision, dimension( * ) a, double precision, dimension( * ) b, double precision, dimension( * ) eig, double precision tol, double precision, dimension( * ) work, integer info)

DSTECH

Purpose:

    !>
    !>    Let T be the tridiagonal matrix with diagonal entries A(1) ,...,
    !>    A(N) and offdiagonal entries B(1) ,..., B(N-1)).  DSTECH checks to
    !>    see if EIG(1) ,..., EIG(N) are indeed accurate eigenvalues of T.
    !>    It does this by expanding each EIG(I) into an interval
    !>    [SVD(I) - EPS, SVD(I) + EPS], merging overlapping intervals if
    !>    any, and using Sturm sequences to count and verify whether each
    !>    resulting interval has the correct number of eigenvalues (using
    !>    DSTECT).  Here EPS = TOL*MAZHEPS*MAXEIG, where MACHEPS is the
    !>    machine precision and MAXEIG is the absolute value of the largest
    !>    eigenvalue. If each interval contains the correct number of
    !>    eigenvalues, INFO = 0 is returned, otherwise INFO is the index of
    !>    the first eigenvalue in the first bad interval.
    !>

Parameters
    N

    !>          N is INTEGER
    !>          The dimension of the tridiagonal matrix T.
    !>

    A

    !>          A is DOUBLE PRECISION array, dimension (N)
    !>          The diagonal entries of the tridiagonal matrix T.
    !>

    B

    !>          B is DOUBLE PRECISION array, dimension (N-1)
    !>          The offdiagonal entries of the tridiagonal matrix T.
    !>

    EIG

    !>          EIG is DOUBLE PRECISION array, dimension (N)
    !>          The purported eigenvalues to be checked.
    !>

    TOL

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

    WORK

    !>          WORK is DOUBLE PRECISION array, dimension (N)
    !>

    INFO

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

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 100 of file dstech.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.