Parameter management utilities

[pelesh]

Managing different solver parameters in Re::Solve becomes a nontrivial task and there is a need for consistent parameter management across all Re::Solve modules. In addition to setting up file I/O for initializing solver parameters, the scope here includes creating a common interface for setting and retrieving parameters for all solver classes and ability to change solver configuration parameters at runtime. The requirements are:

• [ ] Create a generic parameter management interface at the base class, which each derived solver class can populate with its own specific parameters.
• [ ] Parameters can be of different types (integer, floating point, string, etc.).
• [ ] This is core functionality, no additional dependency should be required to implement it.
• [ ] Changing parameters should leave solver in fully functional state with new parameter values.

This draft PR is a proposal how to handle this. Parameter management is implemented only for classes LinSolverIterativeFGMRES and LinSolverIterativeRandGMRES for now.

Closes #96

[stonecoldhughes]

https://github.com/ORNL/ReSolve/issues/96#issuecomment-2362551756

has this utility been tested for all input conditions? Is there logic to detect and report ill-formed combinations of options?

Config options are often represented naturally with a hierarchical data format, and this allows them to be saved for later use. Does that capability exist with this parser? If not, is it desirable?

https://github.com/nlohmann/json is a single header file, so it could be added to the repo once and never bothered with again.

https://github.com/nlohmann/json can parse JSON from a file or the command line directly via stdin if file I/O is undesirable.

Thousands of users have helped refine json.hpp, it is extremely robust and extensively tested.

[stonecoldhughes]

https://en.cppreference.com/w/cpp/language/raii is an idea that applies to configuration - ideally, an object is completely configured and ready to use as soon as it is constructed. Are these configurable solver objects configured with the parsed configuration options in their constructors? Or is the functionality here used to set that up after the fact?

[pelesh]

https://en.cppreference.com/w/cpp/language/raii is an idea that applies to configuration - ideally, an object is completely configured and ready to use as soon as it is constructed. Are these configurable solver objects configured with the parsed configuration options in their constructors? Or is the functionality here used to set that up after the fact?

Since Re::Solve is used for solving series of similar linear systems it is conceivable that one might want to change its parameters at runtime. In that case, Re::Solve would need to ensure that the choice of solver configuration parameters is self-consistent and that correct workspace is allocated.