DSTECT 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

N

          N is INTEGER
          The dimension of the tridiagonal matrix T.

A

          A is DOUBLE PRECISION array, dimension (N)
          The diagonal entries of the tridiagonal matrix T.

B

          B is DOUBLE PRECISION array, dimension (N-1)
          The offdiagonal entries of the tridiagonal matrix T.

SHIFT

          SHIFT is DOUBLE PRECISION
          The shift, used as described under Purpose.

NUM

          NUM is INTEGER
          The number of eigenvalues of T less than or equal
          to SHIFT.

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