TESTING/EIG/ssvdct.f(3) | Library Functions Manual | TESTING/EIG/ssvdct.f(3) |
NAME
TESTING/EIG/ssvdct.f
SYNOPSIS
Functions/Subroutines
subroutine ssvdct (n, s, e, shift, num)
SSVDCT
Function/Subroutine Documentation
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
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.
Author
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