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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