Need 2D-block-parallel form to serial form of matrix transformation interface for future development

[kirk0830]

Background

Some matrix multiplication operations need the full matrix, while presently this interface seems to be absent?

Describe the solution you'd like

A easy-to-use interface for this purpose, will be helpful for representation-related feature development, including integrate QO inside ABACUS rather than use an external python-end post-processing package

Task list only for developers

• [ ] Notice possible changes of behavior
• [ ] Explain the changes of codes in core modules of ESolver, HSolver, ElecState, Hamilt, Operator or Psi

Notice Possible Changes of Behavior (Reminder only for developers)

No response

Notice any changes of core modules (Reminder only for developers)

No response

Notice Possible Changes of Core Modules (Reminder only for developers)

No response

Additional Context

No response

Task list for Issue attackers (only for developers)

• [ ] Review and understand the proposed feature and its importance.
• [ ] Research on the existing solutions and relevant research articles/resources.
• [ ] Discuss with the team to evaluate the feasibility of implementing the feature.
• [ ] Create a design document outlining the proposed solution and implementation details.
• [ ] Get feedback from the team on the design document.
• [ ] Develop the feature following the agreed design.
• [ ] Write unit tests and integration tests for the feature.
• [ ] Update the documentation to include the new feature.
• [ ] Perform code review and address any issues.
• [ ] Merge the feature into the main branch.
• [ ] Monitor for any issues or bugs reported by users after the feature is released.
• [ ] Address any issues or bugs reported by users and continuously improve the feature.

[WHUweiqingzhou]

I also think this interface is quite useful. Actually, in source/module_hamilt_lcao/module_hcontainer/func_transfer.cpp, there are several interfaces between 2D para and serial, but only for HContainer.

[jinzx10]

I second this. I think we definitely need an RAII container for block-cyclic distributed data. Linear algebra operations can also be encapsulated into this container.