[xv,it]=newtonmv(x,f,jf,n,tol)

function [xv,it]=newtonmv(x,f,jf,n,tol)
% Newton's method for solving a system of n non-linear equations
% in n variables.
%
% Example call: [xv,it]=newtonmv(x,f,jf,n,tol)
% Requires an initial approximation column vector x. tol is
% required accuracy. User must define functions f (system equations)
% and jf (partial derivatives). For example of these functions, see
% page 112. xv is the solution vector, the it parameter is number of
% iterations taken. WARNING. The method may fail, for example if
% initial estimates are poor.
%
it=0; xv=x;
fr=feval(f,xv);
while norm(fr)>tol
  Jr=feval(jf,xv);
  xv1=xv-Jr\fr; xv =xv1;
  fr=feval(f,xv);
  it=it+1;
end;