python - NumPy 错误 : The truth value of an array with more than one element is ambiguous. 使用 a.any() 或 a.all()

Question

我正在使用 numpy 编写图像卷积代码:

def CG(A, b, x, imax=10, epsilon = 0.01):
    steps=np.asarray(x)
    i = 0
    r = b - A * x
    d = r.copy()
    delta_new = r.T * r
    delta_0 = delta_new
    while i < imax and delta_new > epsilon**2 * delta_0:
        q = A * d
        alpha = float(delta_new / (d.T * q))
        x = x + alpha * d
        if i%50 == 0:
            r = b - A * x
        else:
            r = r - alpha * q
        delta_old = delta_new
        delta_new = r.T * r
        beta = float(delta_new / delta_old)
        d = r + beta * d
        i = i + 1
        steps = np.append(steps, np.asarray(x), axis=1)
    return steps

我收到以下错误:

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

在线 while i < imax and delta_new > epsilon**2 * delta_0:

谁能告诉我我做错了什么？

Answer 1

看起来 delta_new 和 delta_0 是 Numpy 数组，Numpy 不知道如何比较它们。

举个例子，想象一下如果你拿了两个随机的 Numpy 数组并尝试比较它们:

>>> a = np.array([1, 3, 5])
>>> b = np.array([5, 3, 1])
>>> print(a<b)
array([True, False, False])
>>> bool(a<b)
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

基本上，您必须“选择”如何将所有数组中所有值的比较折叠为一个 bool 值。

>>> (a<b).any()
True

>>> (a<b).all()
False