An electron-positron equation of state based on table interpolation of the Helmholtz free energy is
developed and analyzed. The interpolation scheme guarantees perfect thermodynamic consistency, independent
of the interpolating function. The choice of a biquintic Hermite polynomial as the interpolating
function results in accurately reproducing the underlying Helmholtz free energy data in the table, and
yields derivatives of the pressure, speciÐc entropy, and speciÐc internal energy which are smooth and
continuous. The execution speedÈevaluated across several dierent machine architectures, compiler
options, and modes of operationÈsuggests that the Helmholtz equation of state routine is faster than
any of the Ðve equation of state routines surveyed by Timmes & Arnett. When an optimal balance of
accuracy, thermodynamic consistency, and speed is desirable then the tabular Helmholtz equation of
state is an excellent choice, particularly for multidimensional models of stellar phenomena.