如何将3D矩阵展平为数组？

import numpy as np

def flatten_3d_matrix(matrix_3d):
    # 获取3D矩阵的尺寸
    depth, height, width = matrix_3d.shape
    
    # 创建一维数组
    flattened_array = np.empty(depth * height * width)
    
    # 遍历3D矩阵并添加到一维数组中
    index = 0
    for d in range(depth):
        for h in range(height):
            for w in range(width):
                flattened_array[index] = matrix_3d[d, h, w]
                index += 1
    
    return flattened_array

# 测试代码
matrix_3d = np.array([[[1, 2], [3, 4]], [[5, 6], [7, 8]]])
flattened = flatten_3d_matrix(matrix_3d)
print(flattened)