title: How to make the fluctuation range of three polylines all obvious in same figure by matplotlib?
body: <p>I have three y-value want to show in same figure:</p>
  <pre><code>x=[2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
  y1=[186.1514196056709, 159.12401454010774, 168.58499675415746, 175.84505835379582, 176.46936542235537, 176.8134839358722, 175.46363672676443, 170.82552245819048, 163.39990942665688, 159.88459580397586, 155.3396101804821, 154.46700563801755, 150.79412436478694]
  y2=[0.3016510699429101, 0.26247594932831353, 0.29913169309436605, 0.3053190632425873, 0.3186662404748315, 0.3369847962857457, 
  0.3257363992293248, 0.326098636790218, 0.32587136976180914, 0.309790474192611, 0.30566145932232885, 0.2926688665309739, 0.3127811937803466]
  y3= [1.2213442807894994, 1.2553757513887367, 1.1182748303246677, 1.003606425268881, 0.9987302918527493, 0.9317191492080268, 0.9369917733833383, 0.9985986662450104, 1.0134012327207624, 0.9836205765652832, 1.0239454849518803, 1.0424869369750722, 0.9350958078168375]
  </code></pre>
  <p>however,if I use plt.plot method to show them in same figure, it shows that:
  <a href="https://i.stack.imgur.com/C1Xvw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/C1Xvw.png" alt="enter image description here" /></a></p>
  <p>I want the blue and green line shows like that:
  <a href="https://i.stack.imgur.com/bsgPq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bsgPq.png" alt="enter image description here" /></a></p>
  <p>How to solve it?</p>