function [a,b,fail] = bisect(f,a,b,eps,N)
%
%  Applies the bisection method to the function f on [a,b],
%  f is assumed to be continuous and f(a)*f(b) < 0.
%  Stops when |f(a)| < eps or |f(b)| < eps or |b-a| < eps.
%  Failure is reported (fail = 1) when the accuracy requirement
%  is not satisfied in N steps; otherwise fail = 0 on return.
%
%  Example : 
%  >> [a,b,fail] = bisect('cos',pi/4,2*pi/3,1.0e-4,100)
%
fprintf('running the bisection method...\n');
fprintf('-------------------------------------------\n');
fprintf('    a      b      m     |f(m)|     |b-a|   \n');
fprintf('-------------------------------------------\n');
for i = 1:N 
   m = (a+b)/2;
   fm = feval(f,m);
   if fm*feval(f,a) < 0
      b = m;
   else
      a = m;
   end;
   fprintf('  %4.3f  %4.3f  %4.3f  %.2e  %.2e\n',a,b,m,abs(fm),abs(b-a));
   if (abs(fm) < eps) | ((b-a) < eps)
      fail = 0;
      fprintf('succeeded after %d steps\n', i);
      return;
   end
end
fprintf('failed requirements after %d steps\n', N);
fail = 1;