% Root finding using Secant method
%
function y = fcn(x)
y = x^4 - 5*x^3 - 124*x^2 + 380*x + 1200;
end

% proceed with finding a root:

x1 = 0; % 'Enter first guess of root location;
x2 = 20; % 'Enter second guess of root location;

itermax = 100;      % max # of iterations
iter = 0;
errmax = 0.001;     % convergence tolerance
error = 1;
write('x1  ','x2  ','x3  ','rel error');

while error > errmax & iter < itermax

  iter = iter + 1;
  f1 = fcn(x1);
  f2 = fcn(x2);

  x3 = x2 - f2*(x2-x1) / (f2 - f1);    % here is new root estimate
  

  error = abs((x3 - x2)/x3) * 100;  % find change from previous

  write(x1,'  ',x2,'  ',x3,'  ',error);

  x1 = x2;      % set up for next iteration
  x2 = x3;
end