DOUBLE PRECISION FUNCTION DCBRT(X)
C***BEGIN PROLOGUE  DCBRT
C***DATE WRITTEN   770601   (YYMMDD)
C***REVISION DATE  820801   (YYMMDD)
C***CATEGORY NO.  C2
C***KEYWORDS  CUBE ROOT,DOUBLE PRECISION,ELEMENTARY FUNCTION,ROOT
C***AUTHOR  FULLERTON, W., (LANL)
C***PURPOSE  Computes the d.p. cube root.
C***DESCRIPTION
C
C DCBRT(X) calculates the double precision cube root for
C double precision argument X.
C***REFERENCES  (NONE)
C***ROUTINES CALLED  D1MACH,D9PAK,D9UPAK
C***END PROLOGUE  DCBRT