function x=bissect(a, b, f, tol)

fa = feval(a, f);
fb = feval(b, f);

while (abs(b-a)> tol) 
  mid=(a+b)/2;
  fmid=feval(mid, f);
  if (fa * fmid <=0) then
    b=mid; fb=fmid;
  else
    a=mid; fa=fmid;
  end  
end

x=(a+b)/2;
endfunction