Make the cooling-choice a runtime parameter

[mabruzzo]

This PR builds on #414. (That needs to be merged first)

Overview

At present, there are presently 4 different methods for chemistry or heating & cooling:

(i) chemistry-gpu, (ii) grackle, (iii) tabulated-cloudy, (iv) piecewise-cie¹

At present, this choice is entirely controlled at compile time. The changes in this PR make it possible to specify the tabulated-cooling or piecewise-cie at runtime (the ground-work is laid for specifying both other choices at runtime, but they still require macros).

I also made it possible to switch photo-electric heating on and off (when using tabulated-cooling only).

Description

I had to do a fair bit of refactoring.

The basic control-flow is as follows:

• Before starting the simulation, the main function passes in the ParameterMap (it holds all parsed parameters into) configure_chemistry_callback.
  • if the chemistry.kind parameter is none this will return none (unless the macros for chemistry-gpu or grackle are defined -- in that case the program aborts)
  • if the chemistry.kind parameter is tabulated-cloudy or piecewise-cie this returns a callback to be used for performing heating/cooling
  • if chemistry.kind isn't specified, the default value is picked based on the macros (this is done to avoid breaking tests)
  • If the macros are defined for chemistry-gpu or grackle then this returns nothing (this is a short-term stopgap solution)
• The callback is an object of type std::function<void(Grid3D&)>, which is basically a C++ function-pointer that can wrap functor-objects in addition to regular functions (this is important for retaining the state associated with any functor-objects and properly calling destructors).
• The main function then passes in the callback into Grid.Update_Hydro_Grid. If the callback is not empty, it will always be called.

I had to do some refactoring of src/cooling/cooling_cuda.cu in order to make this select-able at runtime.

Configuration parameters

The new parameters are all in the [cooling] parameter table. (Parameter-tables are introduced in #414 and we leverage functionality to raise errors when there are unused parameters in the cooling group)

The new parameters include:

• cooling.kind
  • allowed values: none, chemistry-gpu, grackle, tabulated-cloudy, piecewise-cie
  • default: defaults to none when no chemistry/heating&cooling parameters are given
  • description: when none, there is no chemistry/heating/cooling
• cooling.data_file
  • description: this can optionally be used to specify a custom path to the data file when using tabulated-cloudy. It is an error to specify this for any other cooling.kind
• chemistry.photoelectric_heating
  • type: boolean
  • default: false
  • description: this can optionally be used to introduce photoelectric-heating when using cooling.kind == tabulated-cloudy. It is an error to specify this for any other cooling.kind
• chemistry.photoelectric_n_av_cgs
  • type: float
  • default: 100.0
  • description: when cooling.kind == tabulated-cloudy and chemistry.photoelectric_heating == true, this can be used to specify the average number-density in the domain in cgs units (which is used to compute impact of photoelectric heating). It is an error to specify when chemistry.photoelectric_heating == false

Footnotes

1. Let me know if you would prefer different names ↩