dstect()

subroutine dstect	(	integer	N,
		double precision, dimension( * )	A,
		double precision, dimension( * )	B,
		double precision	SHIFT,
		integer	NUM
	)

DSTECT

Purpose:

    DSTECT counts the number NUM of eigenvalues of a tridiagonal
    matrix T which are less than or equal to SHIFT. T has
    diagonal entries A(1), ... , A(N), and offdiagonal entries
    B(1), ..., B(N-1).
    See W. Kahan "Accurate Eigenvalues of a Symmetric Tridiagonal
    Matrix", Report CS41, Computer Science Dept., Stanford
    University, July 21, 1966

Parameters

[in]	N	N is INTEGER The dimension of the tridiagonal matrix T.
[in]	A	A is DOUBLE PRECISION array, dimension (N) The diagonal entries of the tridiagonal matrix T.
[in]	B	B is DOUBLE PRECISION array, dimension (N-1) The offdiagonal entries of the tridiagonal matrix T.
[in]	SHIFT	SHIFT is DOUBLE PRECISION The shift, used as described under Purpose.
[out]	NUM	NUM is INTEGER The number of eigenvalues of T less than or equal to SHIFT.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.