CubicSpline: For Entropy and Enthalpy of any phase derived from integration of Csat

The cubic spline fit is implemented as described in:

William H. Press, Brian P. Flannery, Saul A. Teukolsky, William T. Vetterling, Numerical Recipes in C: The Art of Scientific Computing, Cambridge University Press, 1992.

The columns T (temperature), C(heat capacity), and d2C/dT2 (i.e., the second derivative with temperature) correspond to arrays xa, ya, and y2a in the implementation of spline in section 3.3 of the reference (page 116).

The heat capacities are assumed to follow a simple T cubed form below the lowest temperature above T = 0 K. This form is assumed only if the lowest temperature is 20 K or below. Otherwise, the derived thermodynamic functions are not calculated.

Information provided on the Equation Parameters form includes details of extrapolations to T = 0 K for the lowest temperature phase (Example). Evaluation Results: