Add tri-diagonal solve support

[aartbik]

This uses cuSPARSE's legacy API to solve a tri-diagonal matrix direct solve operation (lower diagonal, main diagonal, upper diagonal). This involves a run-time check on DIA (which is more general) to ensure only those three diagonals are used.

[Copilot]

Pull Request Overview

Adds direct tri-diagonal solve support using cuSPARSE’s legacy API with runtime checks for three diagonals in DIA format and updates test and example code.

• Introduce solve_cusparse.h implementing SolveTridiagonalSystem and hooking it into sparse_dia_solve_impl
• Update SolveOp to dispatch to the new DIA solver for I–indexed DIA tensors
• Add tests (SolveDIAI) and an example for tri-diagonal solves

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
test/00_sparse/Dia.cu	Renamed test fixtures and added SolveDIAI tests
include/matx/transforms/solve/solve_cusparse.h	New file implementing cuSPARSE-based tridiagonal solve
include/matx/operators/solve.h	Include solver header and dispatch solve for DIA
examples/sparse_tensor.cu	Example usage demonstrating direct tri-diagonal solve

Comments suppressed due to low confidence (4)

test/00_sparse/Dia.cu:118

• [nitpick] The test suite registration uses MatXFloatNonHalfTypesCUDAExec, which doesn’t match the suite used elsewhere. Ensure this type list is correct or replace it with MatXFloatNonComplexHalfTypesCUDAExec for consistency.

TYPED_TEST_SUITE(DiaSolveSparseTestsAll, MatXFloatNonHalfTypesCUDAExec);

include/matx/operators/solve.h:95

• The dispatch allows both DIAI and DIAJ but the implementation only supports I-index DIA. Restrict this to isDIAI() to prevent runtime errors when using DIAJ.

if constexpr (OpA::Format::isDIAI() || OpA::Format::isDIAJ()) {

include/matx/transforms/solve/solve_cusparse.h:159

• [nitpick] The message 'Tridiagonal solve overwrites rhs' is ambiguous. Consider clarifying it to 'In-place RHS required for tridiagonal solve' to better convey the constraint.

MATX_THROW(matxNotSupported, "Tridiagonal solve overwrites rhs");

test/00_sparse/Dia.cu:184

• The new SolveDIAI test covers real types but omits complex specializations. Add tests for complex value types to ensure full coverage of supported data types.

TYPED_TEST(DiaSolveSparseTestsAll, SolveDIAI) {

[cliffburdick]

/build