Add LinearSolver interface

[alexander-novo]

Description

Add new LinearSolver interface and one implementation using Re::Solve to be used by e.g. Rosenbrock (#479)

Proposed changes

Interface has three lifecycle functions:

• configureSolver called whenever the matrix changes sparsity pattern
• setupSolver called whenever the matrix changes data
• solve to perform a linear solve

Checklist

• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ style guidelines.
• There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.
• I have updated CHANGELOG.md to reflect the changes in this PR. If this is a minor PR that is part of a larger fix already included in the file, state so.

Please see Rosenbrock tests for unit tests.

Further comments

[pelesh]

Brief comments on interfacing with Re::Solve

[pelesh]

I believe there should be a third option reuse_pivot_sequence. Then, this conditional would look something like this:

Suggested change

	if (reuse_factors)
	{
	if (int err = lin_solver_.refactorize())
	return err;
	}
	if (reuse_factors)
	{
	return 0;
	}
	else if (reuse_pivot_sequence)
	{
	if (int err = lin_solver_.refactorize())
	return err;
	}

Might be a good idea to have an enum instead of multiple boolean flags.

[pelesh]

I really don't like setData methods as they are ticking bomb but we still carry them along. How about we create a view constructor to make a shallow copy of the vector:

Suggested change

	ReSolve::vector::Vector resolve_rhs(rhs.getSize());
	ReSolve::vector::Vector resolve_lhs(lhs.getSize());
	if (int err = resolve_rhs.setData(rhs.getData(), memspace_))
	return err;
	if (int err = resolve_lhs.setData(lhs.getData(), memspace_))
	return err;
	if (int err = lin_solver_.solve(&resolve_rhs, &resolve_lhs))
	return err;
	ReSolve::vector::Vector resolve_rhs(rhs.getSize(), rhs.getData());
	ReSolve::vector::Vector resolve_lhs(lhs.getSize(), lhs.getData());
	if (int err = lin_solver_.solve(&resolve_rhs, &resolve_lhs))
	return err;

Even better would be if that constructor is made private and we implement method createVectorView that would invoke such constructor and create vector object that does not own the data.

[pelesh]

This is good to merge. I suggest two minor changes before we merge it:

• Have Rosenbrock class inherit from DynamicSolver class.
• Rebase to the current develop.

[pelesh]

You really don't need this. The SystemSolver class will manage host/device memory spaces under the hood.

Suggested change

	: lin_solver_(lin_solver), memspace_(memorySpaceAsResolve(memspace))
	{
	: lin_solver_(lin_solver)
	{

In the PR the memspace_ is used only to set vector/matrix views. I would just mark those places as @todo to remove them when we improve linear algebra support in GridKit. Better to merge this PR now and address these issues in the next PR.

[pelesh]

Rosenbrock class should inherit from DynamicSolver.

[pelesh]

We are about to release v0.99.3 so this is probably better dependency requirement.

Suggested change

	- [ReSolve](https://github.com/ORNL/ReSolve) == commit `a93fb6571e3542b2fa779983fef0186a034c53c9` (optional)
	- [ReSolve](https://github.com/ORNL/ReSolve) >= 0.99.3 (optional)