code: def plot(self):
      
      plt.ion()
      plt.show()
      x = numpy.linspace(0, 15, 100)
      y = numpy.zeros(x.shape)
      y = self.excite(y, x)
      plt.plot(x, y)
      plt.xlabel('Input')
      plt.ylabel('Persistence')
      plt.title('Sigmoid Activation Function')
docs: plot the activation function