!  Prototype source code for the multinewt subroutine.
!  Add this source code to the module in newton.f90.
!---------------------------------------------------------------------------
    module general_newton
    use precision
    implicit none
    contains
!---------------------------------------------------------------------------
    subroutine multnewt(f,df,x,tol,ierr)
    real(D),intent(inout):: x
    real(D),intent(in):: tol
    integer,intent(out):: ierr
!
!  The interface block below completes the declarations.  Although F is
!  a vector-valued function in principle, it is implemented as a subroutine
!  here.  The function value is returned through the N-vector FCN.
!  Similarly, DF is an NxN matrix, which is returned as a subroutine argument.
!
    interface
       subroutine f(y,n,fcn)
       use precision
       integer,intent(in):: n  ! the number of equations
       real(D),intent(in):: y(n)
       real(D),intent(out):: fcn(n)  ! holds F(y) on return
       end subroutine f
    !------------------
       subroutine df(y,n,dfcn)
       use precision
       integer,intent(in):: n  ! the number of equations
       real(D),intent(in):: y(n)
       real(D),intent(out):: dfcn(n,n)  ! holds the Jacobian matrix on return
       end subroutine df
    end interface
    !------------------
!
!  Local variables and the rest of your code go here.
!
    return
    end subroutine multinewt
!---------------------------------------------------------------------------
    end module general_newton