function x=fib(a,b,n)
  fs(1)=1;
  fs(2)=1;
  for i=3:n+3
    fs(i)=fs(i-2)+fs(i-1);
  endfor
  for i=1:n
    c=a+fs(n-i+1)/fs(n-i+3)*(b-a);
    d=a+fs(n-i+2)/fs(n-i+3)*(b-a);
    if f(c)>f(d)
      a=c;
      else b=d;
    endif
  endfor
  x=c
endfunction