c*******************************************************
      SUBROUTINE FIXPOINT (xstart,nmax,xnew,errfun)
c*******************************************************
c     roots of a nonlinear function FF  -  Fixed point method
c
      IMPLICIT REAL*8 (a-h, o-z)
c
      open(1,file='conv')
      xold=xstart
      fold=FF(xold)
      write(1,*)0,xold,dabs(fold-xold)
c
c___ start iterating _______________
c
      DO niter=1,nmax
         xnew=fold
         fnew=FF(xnew)
         write(*,*) niter,xnew,dabs(xnew-fnew)
         write(1,*) niter,xnew,dabs(xnew-fnew)
c-- Is XR a root?
         IF (dabs(xnew-fnew) .lt. errfun) THEN
            errfun=dabs(xnew-fnew)
            goto 10
         ENDIF
c-- update
      xold=xnew
      fold=fnew
      ENDDO
      stop   'Non-converged !!!! '
 10   close(1)
      RETURN
      END

      include 'testfun.for'