title: Get polynomial coefficients from interpolation splines in R
body: <p>I have a set of measured values that I'd liked to interpolate in <code>R</code> using cubic splines. Since these are just piecewise polynomials I'd subsequently like to integrate the interpolation function <em>algebraically</em>. Therefore I need the coefficients. Is there a way to obtain these?<br>
  Calling <code>splines::interpSpline(foo, bar)$coef</code> doesn't seem to return the actual polynomial coefficients. </p>