TF 2.0 MLP精度始终为零

我写了一个适合给定函数的简单神经网络的最小示例(一个用于回归的多层感知器)。 在培训过程中，损失按预期减少，模型运行良好。然而，精度保持不变，在任何时候都等于0.0，我不明白为什么。我错过了什么? 我想是有一些技术细节阻碍了准确性的更新吧? 训练过程和结果模型可以在这个链接中看到 非常感谢您能提供的任何帮助!,) PS-这里有一个最小的例子来重现这个结果:

from tensorflow.keras import Sequential
from tensorflow.keras.layers import Dense
import numpy as np
import matplotlib.pyplot as plt
from matplotlib import gridspec

# Create TRAINING data
noise = 0.1
N=500
Xt = np.random.uniform(-np.pi, np.pi, size=(N,))
Yt = np.sin(Xt) + noise * np.random.uniform(-1,1,size=Xt.shape)
# Create VALIDATION data
Nv = int(0.1*N)
Xv = np.random.uniform(-np.pi, np.pi, size=(Nv,))
Yv = np.sin(Xv) + noise * np.random.uniform(-1,1,size=Xv.shape)

# Create model
model = Sequential()
model.add( Dense(10, activation='tanh',input_shape=(1,)) )
model.add( Dense(5, activation='tanh') )
model.add( Dense(1, activation=None) )

model.compile(optimizer='adam',
              loss='mse',
              metrics=['accuracy'])

# Fit & evaluate
history = model.fit(Xt, Yt, validation_data=(Xv,Yv),
                            epochs=100,
                             verbose=2)

results = model.evaluate(Xv, Yv,verbose=0)
print('\n\nEvaluating model, loss/acc:', results)


## PLOTS
fig = plt.figure()
gs = gridspec.GridSpec(2, 2)
ax1 = plt.subplot(gs[0,0])              # losses
ax2 = plt.subplot(gs[1,0], sharex=ax1)  # accuracies
ax3 = plt.subplot(gs[:,1])              # data & model

# Plot learning curve
err = history.history['loss']
val_err = history.history['val_loss']
acc = history.history['accuracy']
val_acc = history.history['val_accuracy']
ax1.plot(err,label='loss')
ax1.plot(val_err,label='val_loss')
ax2.plot(acc,label='accuracy')
ax2.plot(val_acc,label='val_accuracy')
ax1.set_ylim(bottom=0)
ax2.set_ylim(bottom=-0.01)
ax1.legend()
ax2.legend()

# Plot test
# Generate "continous" data for pretty test
x = np.linspace(np.min(Xt),np.max(Xt),1000)
y = model.predict(x)

ax3.scatter(Xt, Yt, label='Training')
ax3.scatter(Xv, Yv, c='C2', label='Validation')
ax3.plot(x, y, 'C3-', lw=4, label='Model')
ax3.legend()

fig.tight_layout()
plt.show()

问题来源StackOverflow 地址：/questions/59381284/tf-2-0-mlp-accuracy-always-zero