title: interp3 spline NaN
body: <p>I am having a very weird thing happen with <code>interp3</code> in MATLAB as you can see from the following output:</p>
  
  <blockquote>
    <blockquote>
      <p>interp3(s, vw, rs, vwj, -2.8, 1.5, 1.2)</p>
    </blockquote>
  </blockquote>
  
  <p>ans =</p>
  
  <p>-2.3730e-06</p>
  
  <blockquote>
    <blockquote>
      <p>interp3(s, vw, rs, vwj, -2.8, 1.5, 1.2, 'spline')</p>
    </blockquote>
  </blockquote>
  
  <p>ans =</p>
  
  <p>NaN</p>
  
  <p><code>XI</code>,<code>YI</code>,<code>ZI</code> are all firmly within the grid and linear (default) interpolation seems to work, but when I try a spline I get <code>NaN</code>s for any input arguments.  Weirder, if I specify an <code>extrapval</code> of say 1, if I try a spline I get 1s for all arguments.  Any thoughts?</p>