ssvdct()

subroutine ssvdct	(	integer	N,
		real, dimension( * )	S,
		real, dimension( * )	E,
		real	SHIFT,
		integer	NUM
	)

SSVDCT

Purpose:

 SSVDCT counts the number NUM of eigenvalues of a 2*N by 2*N
 tridiagonal matrix T which are less than or equal to SHIFT.  T is
 formed by putting zeros on the diagonal and making the off-diagonals
 equal to S(1), E(1), S(2), E(2), ... , E(N-1), S(N).  If SHIFT is
 positive, NUM is equal to N plus the number of singular values of a
 bidiagonal matrix B less than or equal to SHIFT.  Here B has diagonal
 entries S(1), ..., S(N) and superdiagonal entries E(1), ... E(N-1).
 If SHIFT is negative, NUM is equal to the number of singular values
 of B greater than or equal to -SHIFT.

 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 bidiagonal matrix B.
[in]	S	S is REAL array, dimension (N) The diagonal entries of the bidiagonal matrix B.
[in]	E	E is REAL array of dimension (N-1) The superdiagonal entries of the bidiagonal matrix B.
[in]	SHIFT	SHIFT is REAL 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.