title: Fitting a parabola using Matlab polyfit
body: <p>I am looking to fit a parabola to the following data.</p>
  
  <pre><code>x = [-10:2:16];
  y = [0.0334,0.0230,0.0145,0.0079,0.0033,0.0009,0.0006,0.0026,0.0067,0.0130,0.0213,0.0317,0.0440,0.0580];
  
  [p,~,~] = polyfit(x,y,2);
  
  x2 = linspace(-10,16,100);
  y2 = polyval(p,x2);
  
  y3 = 0.0003.*x2.^2 -0.0006.*x2 + 0.0011;
  figure
  plot(x,y,'o',x2,y2,x2,y3)
  </code></pre>
  
  <p>However, the fit does not match with the data at all.  After putting the data into excel and fitting using a 2nd order polynomial there, I get a very nice fit.  y = 0.0003x2 - 0.0006x + 0.0011 (excel truncating the coefficients skews the fit a bit). What is happening with polyfit with this data?  </p>