ng the <code>D</code> (<code>deriv</code>) function from the 
    'Ryacas' package (<a href="#Ryacas">Goedman et al., 2016</a>), which provides an 
    interface to the <a href="http://yacas.sourceforge.net">Yacas</a>
    computer algebra system (<a href="#yacas">Pinkus and Winitzki, 2002</a>).
    The <code>xsplineTangentExpr</code> function was written
    to take the output of <code>xsplineFunGenerator</code> and differentiate
    it.  The following code demonstrates (the x-component of) the result from