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A cubic spline is a piecewise cubic polynomial function that is continuous in
value, first derivative and second derivative.
The cubic spline fit underlying this web application is implemented as described in Numerical Recipes.
The columns *T* (temperature), *c*_{sat} (heat capacity), and *d*^{2}*c*_{sat}/*d**T*^{2} (second derivative of *c*_{sat} with temperature) correspond to the tabulated
values described by *x*_{i}, *y*_{i}, and *y*′′_{i} in section 3.3 of the reference.

Between the minimum value in the table and the lower bound of the fit, heat
capacities are assumed to be cubic in temperature (*c*_{sat} = *a**T*^{3}).

Please note that the equations described above are expressed in terms of heat
capacity and **not** in the necessary integral form.

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