Replace numpy with cunumpy

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[max-models]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved all merge conflicts in commit c322ee3. The 8 conflicting files were resolved by keeping the cunumpy/array_backend imports from our branch while adopting the feectools package paths from devel-tiny. Notable changes:

• feectools/fem/tensor.py: adopted the improved MPI-based global grid reconstruction (uses gathered_pcoords from all ranks rather than recomputing on root) and adds proper fig/ax initialization
• feectools/linalg/basic.py: removed duplicate toarray and fixed np.zeros → xp.zeros in SumLinearOperator.toarray
• feectools/feec/global_geometric_projectors.py: added BlockVector to imports (added in devel-tiny)

[Copilot]

Pull request overview

This PR introduces cunumpy as the primary array API (imported as xp) across the codebase, aiming to enable a NumPy/CuPy-style backend switch while keeping existing numerical and MPI/PETSc workflows working.

Changes:

• Added cunumpy to project dependencies and replaced many numpy imports/usages with cunumpy (xp) throughout core, FEM, DDM, and linalg modules.
• Updated several CPU/GPU boundary points (e.g., SciPy sparse/LAPACK interactions, shape/index casting for MPI datatypes) to be more backend-aware.
• Updated a broad set of tests to use cunumpy to match the new public array API.

Reviewed changes

Copilot reviewed 54 out of 54 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
pyproject.toml	Adds cunumpy dependency (NumPy remains listed).
feectools/utilities/utils.py	Switches array ops from numpy to cunumpy (xp).
feectools/utilities/quadratures.py	Switches quadrature allocations/math to xp.
feectools/linalg/utilities.py	Replaces numpy with xp in PETSc/Psydac conversion helpers and small linalg utilities.
feectools/linalg/topetsc.py	Replaces numpy with xp in PETSc export path and indexing helpers.
feectools/linalg/tests/test_stencil_vector.py	Updates tests to use xp for array creation/comparison/random.
feectools/linalg/tests/test_stencil_vector_space.py	Updates tests to use xp arrays.
feectools/linalg/tests/test_stencil_interface_matrix.py	Updates tests to use xp arrays.
feectools/linalg/tests/test_solvers.py	Updates tests to use xp random/norm/equality checks.
feectools/linalg/tests/test_matrix_free.py	Updates tests to use xp random and norms.
feectools/linalg/tests/test_linalg.py	Updates tests to use xp for linear algebra checks and random data.
feectools/linalg/tests/test_kron_stencil_matrix.py	Updates tests to use xp for array ops and equality.
feectools/linalg/tests/test_fft.py	Updates tests to use xp random/allclose/dtype checks.
feectools/linalg/stencil.py	Switches internals to xp, adds backend-aware handling for some CPU/GPU interop points.
feectools/linalg/solvers.py	Switches solver internals from numpy to xp (finfo/infty/allocations).
feectools/linalg/kron.py	Switches Kronecker operators/solvers from numpy to xp and adds some int-casting for shapes/perms.
feectools/linalg/fft.py	Switches FFT wrappers to use xp array types/allocations.
feectools/linalg/direct_solvers.py	Adds backend-aware CPU/GPU transfers around SciPy/LAPACK-based solvers.
feectools/linalg/block.py	Switches block vector/operator utilities to xp, with CPU-side object-array construction for blocks.
feectools/linalg/basic.py	Switches core linear-operator utilities to xp (isscalar, diag/zeros, conjugation).
feectools/fem/vector.py	Switches FEM vector-space checks to xp.
feectools/fem/tests/utilities.py	Switches test utilities to xp for grids/random.
feectools/fem/tests/test_vector_spaces.py	Switches vector-space tests to xp.linspace.
feectools/fem/tests/test_splines.py	Switches spline tests to xp.linspace.
feectools/fem/tests/test_splines_par.py	Switches parallel spline tests to xp.linspace.
feectools/fem/tests/test_spline_interpolation.py	Switches interpolation tests to xp for random/linspace/array ops.
feectools/fem/tests/test_spline_histopolation.py	Switches histopolation tests to xp for arrays/allclose.
feectools/fem/tests/analytical_profiles_1d.py	Switches analytical profiles to xp trig/random.
feectools/fem/tensor.py	Switches tensor FEM evaluation routines to xp array operations; adds a local NumPy import for MPI gather buffers.
feectools/fem/splines.py	Switches spline space implementation to xp and adds backend-aware CPU conversions for solver matrices.
feectools/fem/projectors.py	Switches projector construction to xp for abs/diag/eye.
feectools/fem/partitioning.py	Switches partitioning helpers to xp.
feectools/fem/grid.py	Switches grid utilities to xp.
feectools/feec/hodge.py	Removes unused NumPy import.
feectools/feec/global_geometric_projectors.py	Switches to xp and adds backend-aware handling for matrix construction and indexing.
feectools/feec/derivatives.py	Switches derivative operator implementations to xp.
feectools/ddm/tests/test_multicart_2d.py	Switches DDM tests to xp arrays.
feectools/ddm/tests/test_cart_3d.py	Switches DDM tests to xp arrays.
feectools/ddm/tests/test_cart_2d.py	Switches DDM tests to xp arrays.
feectools/ddm/tests/test_cart_1d.py	Switches DDM tests to xp arrays.
feectools/ddm/petsc.py	Switches PETSc index helper to xp (prod/ravel_multi_index).
feectools/ddm/partition.py	Switches partitioning logic to xp.
feectools/ddm/nonblocking_data_exchanger.py	Switches to xp and adjusts MPI datatype creation argument casting.
feectools/ddm/cart.py	Switches cart decomposition internals to xp and adds int-casting in some MPI-facing areas.
feectools/ddm/blocking_data_exchanger.py	Switches to xp and adjusts MPI datatype creation argument casting.
feectools/core/tests/test_bsplines.py	Switches bspline tests to xp.
feectools/core/tests/test_bsplines_kernel.py	Switches kernel tests to xp.
feectools/core/bsplines.py	Switches bspline public API to xp and adds backend-aware handling in a few utility functions.
feectools/core/bsplines_kernels.py	Minor kernel adjustments (still NumPy-based) for shape handling and index casting.
feectools/api/fem_sum_form.py	Switches sum-form assembly code to xp.
feectools/api/fem_common.py	Switches common FEM helpers (e.g., diag len) to xp.
feectools/api/fem_bilinear_form.py	Switches assembly setup logic (pads/args typing) to xp.

Comments suppressed due to low confidence (2)

feectools/ddm/nonblocking_data_exchanger.py:146

• Translate_ranks is being called with an xp.array. If the cunumpy backend is CuPy, this creates a device array, which mpi4py cannot use for rank translation. Pass a plain Python list (or a NumPy array) of ints instead.

            if self._axis is not None:
                rank_dest = gcomm.group.Translate_ranks(xp.array([rank_dest]), comm.group)[0]

feectools/ddm/blocking_data_exchanger.py:160

• Translate_ranks is being called with an xp.array. If the cunumpy backend is CuPy, this creates a device array, which mpi4py cannot use for rank translation. Pass a plain Python list (or a NumPy array) of ints instead.

            if self._axis is not None:
                rank_dest = gcomm.group.Translate_ranks(xp.array([rank_dest]), comm.group)[0]

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