Interface

The barotropic EOS are represented by objects of type eos_barotr. These objects represent the generic EOS interface and do not implement any EOS. Instead, they forward any request to an actual implementation of a particular EOS. To obtain an eos_barotr object representing a particular EOS, one uses functions such as make_eos_barotr_poly() provided for each type of EOS.

Calling the EOS is a two stage process: first, one needs to specify the state of matter. This can be done either in terms of mass density, or in terms of the pseudo enthalpy \(g\). For this, use the methods at_rho() and at_gm1(). Both return an object of type state. All EOS always provide both forms.

Second, one can use methods of this object to obtain mass density, pseudo enthalpy, pressure, soundspeed, internal specific energy, temperature, and specific entropy. Further, one can use the state object like a boolean variable to check if the state is in the valid regime of the EOS. Trying to compute any of the above from an invalid state will throw an exception. The following snipped demonstrates the EOS use:

auto s = eos.at_rho(rho);
if (s) {
  auto pressure   = s.press()
  auto soundspeed = s.csnd()
}

The functionality above is also provided by another set of EOS methods with names such as press_at_rho(), press_at_gm1(), etc. Those do not throw exceptions when called outside the valid ranges, but instead return NANs. When computing several quantities for the same state, the alternative syntax might be less efficient because the validity has to be checked each time instead of only once as for the primary syntax.

The eos_barotr class also provides methods to query the valid ranges of mass density and pseudo enthalpy. For convenience, there are methods to check if given parameter is inside the valid range.

Tip

The interface objects are designed to be used as ordinary variables, which can be copied around cheaply and without worrying about ownership of any resource allocations. Internally, they just contain a shared pointer to an actual (immutable) implementation.

Note

The EOS interface is thread-safe in the sense that the same EOS oject can be used in multiple threads. Since the EOS implementations are immutable, data-races cannot occur. Copying an EOS object inside a thread is save but might affect performance since the copying is an atomic operation. Passing the EOS inside an innermost loop should better be done by reference instead of value.