 
      SUBROUTINE DDZRO (AE,F,H,N,NQ,IROOT,RE,T,YH,UROUND,B,C,FB,FC,Y)
C***BEGIN PROLOGUE  DDZRO
C***REFER TO  DDRIV3
C     This is a special purpose version of ZEROIN, modified for use with
C     the DDRIV1 package.
C
C     Sandia Mathematical Program Library
C     Mathematical Computing Services Division 5422
C     Sandia Laboratories
C     P. O. Box 5800
C     Albuquerque, New Mexico  87115
C     Control Data 6600 Version 4.5, 1 November 1971
C
C     ABSTRACT
C        ZEROIN searches for a zero of a function F(N, T, Y, IROOT)
C        between the given values B and C until the width of the
C        interval (B, C) has collapsed to within a tolerance specified
C        by the stopping criterion, ABS(B - C) .LE. 2.*(RW*ABS(B) + AE).
C
C     Description of parameters
C        F     - Name of the external function, which returns a
C                double precision result.  This name must be in an
C                EXTERNAL statement in the calling program.
C        B     - One end of the interval (B, C).  The value returned for
C                B usually is the better approximation to a zero of F.
C        C     - The other end of the interval (B, C).
C        RE    - Relative error used for RW in the stopping criterion.
C                If the requested RE is less than machine precision,
C                then RW is set to approximately machine precision.
C        AE    - Absolute error used in the stopping criterion.  If the
C                given interval (B, C) contains the origin, then a
C                nonzero value should be chosen for AE.
C
C     REFERENCES
C       1.  L F Shampine and H A Watts, ZEROIN, A Root-Solving Routine,
C           SC-TM-70-631, Sept 1970.
C       2.  T J Dekker, Finding a Zero by Means of Successive Linear
C           Interpolation, "Constructive Aspects of the Fundamental
C           Theorem of Algebra", edited by B Dejon and P Henrici, 1969.
C***ROUTINES CALLED  DDNTP
C***DATE WRITTEN   790601   (YYMMDD)
C***REVISION DATE  841119   (YYMMDD)
C***CATEGORY NO.  I1A2,I1A1B
C***AUTHOR  KAHANER, D. K., NATIONAL BUREAU OF STANDARDS,
C           SUTHERLAND, C. D., LOS ALAMOS NATIONAL LABORATORY
C***END PROLOGUE  DDZRO
