代码如下，可以正常运行
import tensorflow as tf
w = tf.Variable(tf.constant(5, dtype=tf.float32))
lr = 0.2
epoch = 40
for epoch in range(epoch): # for epoch 定义顶层循环，表示对数据集循环epoch次，此例数据集数据仅有1个w,初始化时候constant赋值为5，循环40次迭代。
with tf.GradientTape() as tape: # with结构到grads框起了梯度的计算过程。
loss = tf.square(w + 1)
grads = tape.gradient(loss, w) # .gradient函数告知谁对谁求导
w.assign_sub(lr * grads) # .assign_sub 对变量做自减 即：w -= lr*grads 即 w = w - lr*grads
print("After %s epoch,w is %f,loss is %f" % (epoch, w.numpy(), loss))
输出结果，感觉这不像报错可以屏蔽吗？
E:\python.ku\Scripts\python.exe E:/Python.woekspace/ai/class1/p13_backpropagation.py
2021-02-19 13:01:10.505569: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cudart64_101.dll
2021-02-19 13:01:13.159923: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library nvcuda.dll
2021-02-19 13:01:14.125061: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1555] Found device 0 with properties:
pciBusID: 0000:01:00.0 name: GeForce GTX 1050 Ti computeCapability: 6.1
coreClock: 1.62GHz coreCount: 6 deviceMemorySize: 4.00GiB deviceMemoryBandwidth: 104.43GiB/s
2021-02-19 13:01:14.125459: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cudart64_101.dll
2021-02-19 13:01:14.135634: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cublas64_10.dll
2021-02-19 13:01:14.148462: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cufft64_10.dll
2021-02-19 13:01:14.152732: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library curand64_10.dll
2021-02-19 13:01:14.167836: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cusolver64_10.dll
2021-02-19 13:01:14.173758: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cusparse64_10.dll
2021-02-19 13:01:14.208480: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cudnn64_7.dll
2021-02-19 13:01:14.209471: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1697] Adding visible gpu devices: 0
2021-02-19 13:01:14.209889: I tensorflow/core/platform/cpu_feature_guard.cc:142] Your CPU supports instructions that this TensorFlow binary was not compiled to use: AVX2
2021-02-19 13:01:14.211074: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1555] Found device 0 with properties:
pciBusID: 0000:01:00.0 name: GeForce GTX 1050 Ti computeCapability: 6.1
coreClock: 1.62GHz coreCount: 6 deviceMemorySize: 4.00GiB deviceMemoryBandwidth: 104.43GiB/s
2021-02-19 13:01:14.211716: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cudart64_101.dll
2021-02-19 13:01:14.211916: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cublas64_10.dll
2021-02-19 13:01:14.212118: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cufft64_10.dll
2021-02-19 13:01:14.212326: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library curand64_10.dll
2021-02-19 13:01:14.212523: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cusolver64_10.dll
2021-02-19 13:01:14.212728: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cusparse64_10.dll
2021-02-19 13:01:14.212928: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library cudnn64_7.dll
2021-02-19 13:01:14.213915: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1697] Adding visible gpu devices: 0
2021-02-19 13:01:14.881988: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1096] Device interconnect StreamExecutor with strength 1 edge matrix:
2021-02-19 13:01:14.882196: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1102] 0
2021-02-19 13:01:14.882322: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1115] 0: N
2021-02-19 13:01:14.883081: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1241] Created TensorFlow device (/job:localhost/replica:0/task:0/device:GPU:0 with 2990 MB memory) -> physical GPU (device: 0, name: GeForce GTX 1050 Ti, pci bus id: 0000:01:00.0, compute capability: 6.1)
After 0 epoch,w is 2.600000,loss is 36.000000
After 1 epoch,w is 1.160000,loss is 12.959999
After 2 epoch,w is 0.296000,loss is 4.665599
After 3 epoch,w is -0.222400,loss is 1.679616
After 4 epoch,w is -0.533440,loss is 0.604662
After 5 epoch,w is -0.720064,loss is 0.217678
After 6 epoch,w is -0.832038,loss is 0.078364
After 7 epoch,w is -0.899223,loss is 0.028211
After 8 epoch,w is -0.939534,loss is 0.010156
After 9 epoch,w is -0.963720,loss is 0.003656
After 10 epoch,w is -0.978232,loss is 0.001316
After 11 epoch,w is -0.986939,loss is 0.000474
After 12 epoch,w is -0.992164,loss is 0.000171
After 13 epoch,w is -0.995298,loss is 0.000061
After 14 epoch,w is -0.997179,loss is 0.000022
After 15 epoch,w is -0.998307,loss is 0.000008
After 16 epoch,w is -0.998984,loss is 0.000003
After 17 epoch,w is -0.999391,loss is 0.000001
After 18 epoch,w is -0.999634,loss is 0.000000
After 19 epoch,w is -0.999781,loss is 0.000000
After 20 epoch,w is -0.999868,loss is 0.000000
After 21 epoch,w is -0.999921,loss is 0.000000
After 22 epoch,w is -0.999953,loss is 0.000000
After 23 epoch,w is -0.999972,loss is 0.000000
After 24 epoch,w is -0.999983,loss is 0.000000
After 25 epoch,w is -0.999990,loss is 0.000000
After 26 epoch,w is -0.999994,loss is 0.000000
After 27 epoch,w is -0.999996,loss is 0.000000
After 28 epoch,w is -0.999998,loss is 0.000000
After 29 epoch,w is -0.999999,loss is 0.000000
After 30 epoch,w is -0.999999,loss is 0.000000
After 31 epoch,w is -1.000000,loss is 0.000000
After 32 epoch,w is -1.000000,loss is 0.000000
After 33 epoch,w is -1.000000,loss is 0.000000
After 34 epoch,w is -1.000000,loss is 0.000000
After 35 epoch,w is -1.000000,loss is 0.000000
After 36 epoch,w is -1.000000,loss is 0.000000
After 37 epoch,w is -1.000000,loss is 0.000000
After 38 epoch,w is -1.000000,loss is 0.000000
After 39 epoch,w is -1.000000,loss is 0.000000
Process finished with exit code 0
