说明：  手写数字数据集,该数据集包含60,000个用于训练的示例和10,000个用于测试的示例。这些数字已经过尺寸标准化并位于图像中心，图像是固定大小(28x28像素)，其值为0到1。
(mnist datasets, which contains 60000 samples for training and 10000 samples for testing. These numbers are dimensionally standardized and located in the center of the image, which is a fixed size (28x28 pixels) with a value of 0 to 1.)