int.f77

      FUNCTION SQRT_ITER(GUESS,X)
      DOUBLE PRECISION SQRT_ITER,GUESS,X,IMPROVE
      LOGICAL          GOOD_ENOUGH
      EXTERNAL         GOOD_ENOUGH,IMPROVE
   10 GUESS=IMPROVE(GUESS,X)
      IF (.NOT.GOOD_ENOUGH(GUESS,X)) GOTO 10
      SQRT_ITER=GUESS
      END

      FUNCTION IMPROVE(GUESS,X)
      DOUBLE PRECISION IMPROVE,GUESS,X,AVERAGE
      EXTERNAL         AVERAGE
      IMPROVE=AVERAGE(GUESS,X/GUESS)
      END

      FUNCTION AVERAGE(X,Y)
      DOUBLE PRECISION AVERAGE,X,Y
      AVERAGE=(X+Y)/2.0D0
      END

      FUNCTION GOOD_ENOUGH(GUESS,X)
      LOGICAL          GOOD_ENOUGH
      DOUBLE PRECISION GUESS,X,TOL
      PARAMETER       (TOL=0.001D0)
      GOOD_ENOUGH=DABS(GUESS*GUESS-X).LT.TOL
      END

      FUNCTION MYSQRT(X)
      DOUBLE PRECISION MYSQRT,X,GUESS,SQRT_ITER
      EXTERNAL         SQRT_ITER
      DOUBLE PRECISION ZERO,ONE
      PARAMETER(ZERO=0.0D0,ONE=1.0D0)
C
C XXX COMPUTING THE SQRT OF ZERO RESULTS IN DIVIDE BY ZERO
C
      MYSQRT=ZERO
      IF (X.EQ.ZERO) RETURN
      IF (X.LT.ZERO) X=-X
      GUESS=ONE
      MYSQRT=SQRT_ITER(GUESS,X)
      END

      IMPLICIT NONE
      DOUBLE PRECISION REZ,X,XMIN,XMAX,STEP
      DATA REZ/0.0D0/,STEP/.001D0/,XMIN/0.0D0,XMAX/10000.0D0/
      DOUBLE PRECISION MYSQRT
      EXTERNAL         MYSQRT
      DO 10 X=XMIN,XMAX,STEP
        REZ=REZ+MYSQRT(X)*STEP
   10 CONTINUE
      PRINT*,REZ
      END