ssvdct.f - Man Page

subroutine ssvdct (n, s, e, shift, num)
SSVDCT

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

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 of dimension (N-1)
          The superdiagonal entries of the bidiagonal matrix B.

SHIFT

          SHIFT is REAL
          The shift, used as described under Purpose.

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.

Definition at line 86 of file ssvdct.f.