SUBROUTINE DLASQ4( N, Q, E, TAU, SUP ) INTEGER N DOUBLE PRECISION SUP, TAU DOUBLE PRECISION E( * ), Q( * )
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 .
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