def goldSection eps global counter phi 618034 x1 phi x2 phi y1 x1 y2 x

def goldSection(a, b, eps, f):
    global counter
    phi = 1.618034
    
    x1 = b - (b - a)/phi
    x2 = a + (b - a)/phi 

    y1 = f(x1)
    y2 = f(x2)
        
    if y1 >= y2:
        a = x1
    else: 
        b = x2
  
    
    if abs(b - a) < eps:
        return (a + b)/2
    else:
        counter += 1
        return goldSection(a, b, eps, f)