title: Interpolation between two curves (matlab)
body: <p>Ok guys. I have the following problem:</p>
  
  <p>I have the data of the following plot.
  <img src="https://i.stack.imgur.com/uX4qK.png" alt="enter image description here"></p>
  
  <p>So the data file of this plot contains three columns.
  The 2nd and 3rd ones the x,y points. And the 1st one is to which system those points belong. 
  In this case the red ones are for the system of 20 years. The blue ones for the 30 years. </p>
  
  <p>What I want to find is the curve at 25 years. So if I plot it it should be between the red and blue curves.</p>
  
  <p>I have no idea how interpolate the data in order to obtain what I want. Actually I want to have for 21,22,...29 years, I guess if we can find it for a time in between these two, then the method should work for any time between 20 and 30.</p>
  
  <p>PS: I guess the interpolation for each curve (in this case red or blue one) is quite easy. Just using interp1(x,y,xx) will work. But what happened with the other "dimension" (M)</p>
  
  <p>The data.</p>
  
  <pre><code>20.0000    3.4076         0
  20.0000    3.4226   99.5405
  20.0000    3.4701  196.3360
  20.0000    3.5592  287.0781
  20.0000    3.6248  328.8516
  20.0000    3.6643  348.3373
  20.0000    3.7091  367.2823
  20.0000    3.7591  385.4784
  20.0000    3.8077  402.7170
  20.0000    3.8957  437.5221
  20.0000    4.0314  506.9907
  30.0000    3.6335         0
  30.0000    3.6373   49.8884
  30.0000    3.6488   99.5405
  30.0000    3.6685  148.5936
  30.0000    3.7363  243.2204
  30.0000    3.7876  287.7398
  30.0000    3.8537  329.6097
  30.0000    3.8935  349.9452
  30.0000    3.9384  368.9776
  30.0000    3.9892  387.2576
  30.0000    4.0410  404.5759
  30.0000    4.1350  439.5416
  30.0000    4.2153  474.2420
  30.0000    4.2813  509.3309
  </code></pre>