Make Vector::copyDataTo able to copy from device to host and vice versa

[shakedregev]

Description

Current implementation of Vector::copyDataTo methods allows for copying from host-to-host and device-to-device only. If one needs to copy from host to device one needs an additional copy operation. Need to modify Vector::copyDataTo so it can copy data from any memory space to any memory space, similar as Vector::copyDataFrom methods.

Proposed changes

My changes allow the source and memory space to be different. I also addressed naming issues and syncing issues.

Checklist

• All tests pass (make test and make test_install per testing instructions). Code tested on
  • CPU backend
  • CUDA backend
  • HIP backend
• I have manually run the non-experimental examples and verified that residuals are close to machine precision. (In your build directory run:
  ./examples/<your_example>.exe -h to get instructions how to run examples). Code tested on:
  • CPU backend
  • CUDA backend
  • HIP backend
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows Re::Solve 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.

Further comments

I noticed some issues that I left to not explode the scope of the PR. We should follow up on these.

1. copyDataFrom has similar naming and potentially syncing issues
2. GramSchmidt is littered with deviceSynchronize() seemingly arbitrarily
3. Vector tests have some commented tests.

[alexander-novo]

with the recent change to getData being const is it possible to mark these functions as const?

[pelesh]

I would suggest renaming copyDataFrom --> copyFromExternal in this PR. Otherwise we leave vector methods names in "asymmetric" state.

Other than that, this looks good!

[pelesh]

with the recent change to getData being const is it possible to mark these functions as const?

It is, but would require cleaning up the code where the sloppy data movement was used.

[shakedregev]

Thanks for the feedback. Fixed. Please re-review.