SSTECT
Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
November 2006
November 2006
Purpose
SSTECT 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
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
Arguments
| N |
(input) INTEGER
The dimension of the tridiagonal matrix T.
|
| A |
(input) REAL array, dimension (N)
The diagonal entries of the tridiagonal matrix T.
|
| B |
(input) REAL array, dimension (N-1)
The offdiagonal entries of the tridiagonal matrix T.
|
| SHIFT |
(input) REAL
The shift, used as described under Purpose.
|
| NUM |
(output) INTEGER
The number of eigenvalues of T less than or equal
to SHIFT. |