The UTri Equation of State Table Format

For at least 60 years, tabular equation of state models have been ubiquitous in physics codes for their acceleration of state evaluations over direct calculations of analytic equations, or more costly computational models. These tables most commonly rely on interpolation of pressure and internal energy across a Cartesian grid in density-temperature space, as seen in the well known SESAME format and it derivatives. Herein a different approach is taken, instead using interpolation on an unstructured triangular grid, in short, a UTri table. The UTri format allows optimizing the dominant code path of a physics code, e.g. by tabulating in density-internal energy space, naturally may mesh curved phase boundaries, and easily adapts to meet table accuracy criteria. Examples will demonstrate these benefits with comparison to typical SESAME table usage and the format will be described.