LAPACK  3.5.0
LAPACK: Linear Algebra PACKage
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ssvdct.f File Reference

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Functions/Subroutines

subroutine ssvdct (N, S, E, SHIFT, NUM)
 SSVDCT More...
 

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
[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.
Date
November 2011

Definition at line 88 of file ssvdct.f.

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