DLASQ4 (3lapack)

DLASQ4 estimates TAU, the smallest eigenvalue of a matrix

SYNOPSIS

  SUBROUTINE DLASQ4( N, Q, E, TAU, SUP )

      INTEGER        N

      DOUBLE         PRECISION SUP, TAU

      DOUBLE         PRECISION E( * ), Q( * )

PURPOSE

     DLASQ4 estimates TAU, the smallest eigenvalue of a matrix. This
     routine improves the input value of SUP which is an upper bound
     for the smallest eigenvalue for this matrix .

ARGUMENTS

  N       (input) INTEGER
          On entry, N specifies the number of rows and columns in the matrix.
          N must be at least 0.

  Q       (input) DOUBLE PRECISION array, dimension (N)
          Q array

  E       (input) DOUBLE PRECISION array, dimension (N)
          E array

  TAU     (output) DOUBLE PRECISION
          Estimate of the shift

  SUP     (input/output) DOUBLE PRECISION
          Upper bound for the smallest singular value