DLASQ6  -  compute one dqd (shift equal to zero) transform
       in ping-pong form, with protection against  underflow  and
       overflow


SYNOPSIS

       SUBROUTINE DLASQ6( I0,  N0, Z, PP, DMIN, DMIN1, DMIN2, DN,
                          DNM1, DNM2 )

           INTEGER        I0, N0, PP

           DOUBLE         PRECISION DMIN, DMIN1, DMIN2, DN, DNM1,
                          DNM2

           DOUBLE         PRECISION Z( * )


PURPOSE

       DLASQ6 computes one dqd (shift equal to zero) transform in
       ping-pong form,  with  protection  against  underflow  and
       overflow.


ARGUMENTS

       I0    (input) INTEGER
             First index.

       N0    (input) INTEGER
             Last index.

       Z     (input) DOUBLE PRECISION array, dimension ( 4*N )
             Z  holds  the qd array. EMIN is stored in Z(4*N0) to
             avoid an extra argument.

       PP    (input) INTEGER
             PP=0 for ping, PP=1 for pong.

       DMIN  (output) DOUBLE PRECISION
             Minimum value of d.

             DMIN1 (output) DOUBLE PRECISION Minimum value of  d,
             excluding D( N0 ).

             DMIN2  (output) DOUBLE PRECISION Minimum value of d,
             excluding D( N0 ) and D( N0-1 ).

       DN    (output) DOUBLE PRECISION
             d(N0), the last value of d.

       DNM1  (output) DOUBLE PRECISION
             d(N0-1).

       DNM2  (output) DOUBLE PRECISION
             d(N0-2).


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