Implement Kronecker product for AbstractDeviceSparseMatrix

[Copilot]

Implementation Plan for Kronecker Product

• Explore repository structure and understand the codebase
• Run tests to verify current state
• Research how kron works with sparse matrices in Julia
• Implement kron for each sparse matrix format
  • Add kron kernel to matrix_coo_kernels.jl
  • Add kron(COO, COO) in matrix_coo.jl
  • Add kron(CSC, CSC) in matrix_csc.jl (converts via COO)
  • Add kron(CSR, CSR) in matrix_csr.jl (converts via COO)
  • Remove synchronize() call after kernel launch
  • Remove generic AbstractDeviceSparseMatrix method
• Integrate tests into each format's test file
  • Use rectangular random matrices (30×25 and 20×15)
  • Add tests to matrix_coo, matrix_csc, and matrix_csr test files
  • Remove standalone kron test file
• Clean up and test

Summary

Refactored the kron implementation based on review feedback:

1. Removed synchronize() call - The kernel doesn't need explicit synchronization
2. Removed generic method - No longer have kron(AbstractDeviceSparseMatrix, AbstractDeviceSparseMatrix)
3. Format-specific methods - Defined kron(COO, COO), kron(CSC, CSC), and kron(CSR, CSR) in their respective files
4. Kernel location - Moved to matrix_coo_kernels.jl instead of standalone file
5. Test integration - Tests are now part of each format's test suite with proper rectangular matrices
6. Cleanup - Removed standalone kron.jl and kron_kernels.jl files

The implementation now follows the repository's structure and conventions.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Implemente Kronecker product between two AbstractDeviceSparseMatrix</issue_title>
<issue_description>Implement the method kron(A::AbstractDeviceSparseMatrix, B::AbstractDeviceSparseMatrix) efficiently.

Perhaps one could convert them to COO format, which should be then trivial to do. But better to keep their original formats if possible.</issue_description>

<agent_instructions>Of course, the solution of converting them to CPU arrays is not allowed, as this is a backend specific library.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Implemente Kronecker product between two AbstractDeviceSparseMatrix #19

---

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[codecov]

Codecov Report

❌ Patch coverage is 89.13043% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.91%. Comparing base (9bb1350) to head (0b16c5d).

Files with missing lines	Patch %	Lines
src/matrix_coo/matrix_coo_kernels.jl	82.35%	3 Missing ⚠️
src/conversions/conversion_kernels.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
+ Coverage   84.34%   84.91%   +0.57%     
==========================================
  Files          13       13              
  Lines         728      769      +41     
==========================================
+ Hits          614      653      +39     
- Misses        114      116       +2     

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[albertomercurio]

@copilot the tests are failing. This is because you are using synchronize after calling the kernel, but you don't need it actually.

Also, I like that you defined the method for CSC, but I don't like that you defined a generic method for two AbstractDeviceSparseMatrix. You should only define the methods for CSC-CSC, CSR-CSR and COO-COO in their respective files. Also, you can write the kron coo kernel directly in the coo kernels file, rather than creating a new file.

Finally, you don't need to define a new shared function for the tests specific for kron. You can add a new test set on each format. Also, don't use manually set matrices, but use rectangular random matrices of a sufficiently large size, like in the already existing tests.

[Copilot]

@copilot the tests are failing. This is because you are using synchronize after calling the kernel, but you don't need it actually.

Also, I like that you defined the method for CSC, but I don't l...

I've refactored the implementation:

1. ✅ Removed synchronize() call after kernel launch
2. ✅ Removed generic kron(AbstractDeviceSparseMatrix, AbstractDeviceSparseMatrix) method
3. ✅ Defined separate methods: kron(COO, COO), kron(CSC, CSC), and kron(CSR, CSR) in their respective files (matrix_coo.jl, matrix_csc.jl, matrix_csr.jl)
4. ✅ Moved kernel to matrix_coo_kernels.jl (removed standalone kron_kernels.jl)
5. ✅ Integrated tests into each format's test file with rectangular random matrices (30×25 and 20×15)
6. ✅ Removed standalone test file

Changes in commit e37ecbc

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