function [x,f,ea,iter]=newtmult(func,x0,es,maxit,varargin)
% newtmult: Newton-Raphson root zeroes nonlinear systems
% [x,f,ea,iter]=newtmult(func,x0,es,maxit,p1,p2,...):
% uses the Newton-Raphson method to find the roots of
% a system of nonlinear equations
% input:
% func = name of function that returns f and J
% x0 = initial guess
% es = desired percent relative error (default = 0.0001%)
% maxit = maximum allowable iterations (default = 50)
% p1,p2,... = additional parameters used by function
% output:
% x = vector of roots
% f = vector of functions evaluated at roots
% ea = approximate percent relative error (%)
% iter = number of iterations
if nargin<2,error('at least 2 input arguments required'),end
if nargin<3|isempty(es),es=0.0001;end
if nargin<4|isempty(maxit),maxit=50;end
iter = 0;
x=x0;
while (1)
[J,f]=func(x,varargin{:});
dx=J\f;
x=x-dx;
iter = iter + 1;
ea=100*max(abs(dx./x));
if iter>=maxit|ea<=es, break, end
end
end