dlasq3.f - Man Page

subroutine dlasq3 (i0, n0, z, pp, dmin, sigma, desig, qmax, nfail, iter, ndiv, ieee, ttype, dmin1, dmin2, dn, dn1, dn2, g, tau)
DLASQ3 checks for deflation, computes a shift and calls dqds. Used by sbdsqr.

DLASQ3 checks for deflation, computes a shift and calls dqds. Used by sbdsqr.  

Purpose:

 DLASQ3 checks for deflation, computes a shift (TAU) and calls dqds.
 In case of failure it changes shifts, and tries again until output
 is positive.

Parameters

I0

          I0 is INTEGER
         First index.

N0

          N0 is INTEGER
         Last index.

Z

          Z is DOUBLE PRECISION array, dimension ( 4*N0 )
         Z holds the qd array.

PP

          PP is INTEGER
         PP=0 for ping, PP=1 for pong.
         PP=2 indicates that flipping was applied to the Z array
         and that the initial tests for deflation should not be
         performed.

DMIN

          DMIN is DOUBLE PRECISION
         Minimum value of d.

SIGMA

          SIGMA is DOUBLE PRECISION
         Sum of shifts used in current segment.

DESIG

          DESIG is DOUBLE PRECISION
         Lower order part of SIGMA

QMAX

          QMAX is DOUBLE PRECISION
         Maximum value of q.

NFAIL

          NFAIL is INTEGER
         Increment NFAIL by 1 each time the shift was too big.

ITER

          ITER is INTEGER
         Increment ITER by 1 for each iteration.

NDIV

          NDIV is INTEGER
         Increment NDIV by 1 for each division.

IEEE

          IEEE is LOGICAL
         Flag for IEEE or non IEEE arithmetic (passed to DLASQ5).

TTYPE

          TTYPE is INTEGER
         Shift type.

DMIN1

          DMIN1 is DOUBLE PRECISION

DMIN2

          DMIN2 is DOUBLE PRECISION

DN

          DN is DOUBLE PRECISION

DN1

          DN1 is DOUBLE PRECISION

DN2

          DN2 is DOUBLE PRECISION

G

          G is DOUBLE PRECISION

TAU

          TAU is DOUBLE PRECISION

         These are passed as arguments in order to save their values
         between calls to DLASQ3.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 179 of file dlasq3.f.