title: Adding or multiplying cubic splines obtained with scipy.interpolate.CubicSpline
body: <p>I have a function that wants to combine multiple spectra (x,y) with addition and multiplication. For each of those spectra I have cubic spline objects (scipy.interpolate.CubicSpline). When I try to run my function I get this error:</p>
  
  <ul>
  <li>TypeError: unsupported operand type(s) for -: 'int' and 'CubicSpline'</li>
  </ul>
  
  <p>I've searched this site and google for how to operate on type cubic splines (tried to use:</p>
  
  <ul>
  <li>tck = scipy.interpolate.splrep()</li>
  <li>Function = scipy.interpolate.PPoly.from_spline(tck)</li>
  </ul>
  
  <p>...but I can't understand how to handle and manipulate these objects to be used with mathematical operations.) I can't just add the raw spectra without splines because they don't all share common 'x' values.</p>
  
  <p>I can plot them and integrate them separately, so what form do I need to put them into to use simple math operators (multiply two splines, add splines)?</p>