报错为： raise RuntimeError('The Session graph is empty.  Add operations to the '

RuntimeError: The Session graph is empty.  Add operations to the graph before calling run().

它说图为空，这是为什么

代码为：

import numpy as np

import matplotlib.pyplot as plt

import tensorflow as tf

x=np.linspace(-7,7,180)

def sigmoid(inputs):

    y=[1/float(1+np.exp(-x)) for x in inputs]

    return y

def relu(inputs):

    y=[x*(x>0) for x in inputs]

    return y

def tanh(inputs):

    y=[(np.exp(x)-np.exp(-x))/float(np.exp(x)+np.exp(-x)) for

       x in inputs]

    return y

def softplus(inputs):

    y=[np.log(1+np.exp(x)) for x in inputs]

    return y

y_sigmoid=sigmoid(x)

y_relu=relu(x)

y_tanh=tanh(x)

y_softplus=softplus(x)

sess=tf.Session()

m1,m2,m3,m4=sess.run([y_sigmoid,y_relu,y_tanh,y_softplus])

plt.subplot(221)

plt.plot(x,m1,c="red",label="sigomid")

plt.ylim(-0.2,1.2)

plt.legend(loc="best")

plt.subplot(222)

plt.plot(x,m2,c="green",label="relu")

plt.ylim(-1,6)

plt.legend(loc="best")

plt.subplot(223)

plt.plot(x,m3,c="red",label="tanh")

plt.ylim(-1.3,1.3)

plt.legend(loc="best")

plt.subplot(224)

plt.plot(x,m4,c="red",label="soft")

plt.ylim(-1,6)

plt.legend(loc="best")

plt.show()

sess.close()