title: Are there any C# math libraries that do interpolation / extrapolation
body: <p>For example, I have points</p>
  
  <p><strong>Y X</strong><br>
  100  50<br>
  90   43<br>
  80   32  </p>
  
  <p>need to solve for y = 50</p>
  
  <p>or</p>
  
  <p><strong>Y X</strong><br>
  1/1/2009  100<br>
  1/3/2009  97<br>
  1/4/2009  94<br>
  1/5/2009  92<br>
  1/6/2009  91<br>
  1/7/2009  89  </p>
  
  <p>need to solve for y = 1/23/2009</p>