stuff.py

def armijo_step(xi,alpha,beta,gamma):
    k = 1
    c = 0
    s = - grad(xi)

    left lambda: cost(xi + alpha*k*s) - cost(xi)
    right lambda: alpha*k*gamma*np.dot(grad(xi).T,alpha*s)

    while left() > right():
        k = k * beta
        print(str(alpha*k))
        print(str(c))
        c = c + 1
    print(str(c))
    return alpha*k