title: Keeping the color scaling the same for different plots - Python
body: <p>I am working with Python and matplotlib. 
  I am doing a continuously plot of some data I get from a spectrum analyser. So with every new step of my loop a new piece is added to my plot. </p>
  
  <p>But i just realised that the color scaling doesn't remain the same. So sometimes if the data are a little different it makes a completely new scaling: </p>
  
  <p><a href="https://i.stack.imgur.com/x1vba.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/x1vba.png" alt="enter image description here"></a></p>
  
  <p>You can recognise it at the big red circle in the middle. The value of the entries for the red circle are all zeros. So normally it should have the same color with every new iteration. But as you can see, if you look closely, this isn't the case. Sometimes the red is a little bit darker. </p>
  
  <p>I already set my <code>vmin</code>to -100 and my <code>vmax</code> to 0 : </p>
  
  <pre><code> while True: 
    ... #some code 
  
    a = np.linspace( (i*np.pi/8-np.pi/16)%(np.pi*2) ,( i*np.pi/8+np.pi/16)%(np.pi*2) , 2)#Angle, circle is divided into 16 pieces
    b = np.linspace(start -scaleplot, stop,801) #points of the frequency + 200  more points to gain the inner circle
    A, B = np.meshgrid(a, longzeroarray)
  
    ax.contourf(a, b, B , cmap=cm.jet, vmin=-100, vmax=0)
  
    plt.draw()
  </code></pre>
  
  <p>I hope you have some helpful ideas. </p>