A Method for the Selection of a Functional Form for a Thermodynamic Equation of State Using Weighted Linear Least Squares Stepwise Regression
In studies to determine equations of state for thermodynamic fluids, a number of polynomial forms have been suggested for use in fitting experimental measurements. The purpose of this study was to develop a method for establishing a rational choice of the terms to be included in an equation of state with a large number of adjustable coefficients. The methods presented here were developed for use in the determination of an equation of state for oxygen and nitrogen. However, these methods are generally applicable in studies for determining an optimum polynomial equation for fitting to a large number of data points. The equation of state derived for oxygen and nitrogen  has subsequently been applied to additional fluids by others (e.g., by McCarty ) for methane and appears to be useful for many fluids. The statistical analysis of the results of the least squares fit to determine a thermodynamic equation of state should be considered an adjunct to the calculation of properties from the formulation for direct comparison to experimental data to determine the quality of the representation of the data.
KeywordsCritical Region Stepwise Regression Stepwise Multiple Regression Adjustable Coefficient Thermodynamic Equation
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