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function [x, xlist, iter] = nr (f, df, x0, tol, maxit)
%Root of f(x)=0 by Newton-Raphson's method.
%Method terminates when relative change > tol
%or maximum number exceeds of iterations.
if nargin < 3, error('Insufficient input \n'); end;
if nargin < 4, tol=eps; end;
if nargin < 5, maxit=50; end;
x = x0;
iter = 0;
xdiff = inf;
xlist = x;
while xdiff >= tol
    iter = iter + 1;
    xold = x;
    x = x-feval(f,x)/feval(df,x);
    xdiff = abs(x-xold)/abs(x);
    xlist = [xlist;x];
    if iter >= maxit, error('Not converged after maxit iterations.');
    end;
end;