FreeEOS is a software library for calculating an equation of state for conditions in stellar interiors. The latest stable version of this library source code, FreeEOS-2.2.1, has been released on 2008-07-08.

FreeEOS-2.2.1 is a bug-fix release for the FreeEOS-2.2.0 release. FreeEOS-2.2.0 required substantial code reorganization to scale results to avoid underflows in calculations of intermediate quantities; improve the usual Newton-Raphson technique for solving the EOS; and implement the alternative BFGS minimization technique as an emergency alternative when the normal Newton-Raphson method fails to converge. The result worked well when compiled by g77 version 3.3.5 for the EOS1 option suite and when density and temperature were the independent variables (kif=2), but wider testing on other platforms and for different option suites showed a number of independent bugs had been introduced by the 2.2.0 code reorganization. As a result of these bugs, FreeEOS-2.2.0 is no longer a recommended release. However, the current release fixes all those bugs and also produces negligible differences with results from FreeEOS-2.1.0, the last recommended release.

The major option suites (PTEH, GEFF, SIREFF, MDH, EOS1, EOS2, EOS3, and EOS4) for kif=0 (fl the independent variable), kif=1 (ln Ptotal the independent variable), and kif=2 (ln rho the independent variable) now all give good results for a log T = 4.9 isotherm when the source code is compiled by gfortran-4.3.1. EOS1 continues to work for a wide density/temperature range for kif=2 (as illustrated by the above negligible differences with prior results) when the source code is compiled by gfortran-4.3.1. Additional spot checks show good results for source code compiled with g77-3.4.6.

In short, FreeEOS-2.2.1 works without any obvious problems on the platforms/compilers accessible to me for a wide range of option suites and conditions. Testing on other platforms is requested.

The robustness of the FreeEOS convergence has been substantially improved for FreeEOS-2.2.0 and subsequent versions. The result is that newer versions of FreeEOS converge for densities at least 1 dex higher than the calculational limit for FreeEOS-2.1.0 or previous versions. However, preliminary calculations for this newly accessible region indicate deficiencies in the EOS1 free-energy model for high-density/low-temperature conditions near the main-sequence hydrogen-burning limit (see Paper V for the details). A substantial adjustment of the EOS1 free-energy model is in progress with the goal of reducing or overcoming these deficiencies while simultaneously maintaining or improving the existing fit of EOS1 results to the OPAL EOS_2005 results.

N.B. If you are new to FreeEOS or haven't built a recent version of FreeEOS you need to be aware that FreeEOS-2.1.0 and all subsequent versions must be built with the new CMake-based build system. (You use the "cmake" command rather than the "configure" command and follow that "cmake" command with the usual "make" and "make install". See the README file for details about how to use this new build system.)

Download the FreeEOS-2.2.1 tarball from here and have a look at the release notes and ChangeLog here.

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Copyright © 2008 Alan W. Irwin

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