Simplify spmatrix _set_many (#42)

* Simplify spmatrix _set_many

tdgl/finite_volume/operators.py

@@ -3,7 +3,6 @@
 
 import numpy as np
 import scipy.sparse as sp
-from scipy.sparse._sparsetools import csr_sample_offsets
 
 try:
     import cupy  # type: ignore
@@ -16,25 +15,6 @@
 from .mesh import Mesh
 
 
-def _get_spmatrix_offsets(
-    spmatrix: sp.spmatrix, i: np.ndarray, j: np.ndarray, n_samples: int
-) -> np.ndarray:
-    """Calculates the sparse matrix offsets for a set of rows ``i`` and columns ``j``."""
-    # See _set_many() at
-    # https://github.com/scipy/scipy/blob/3f9a8c80e281e746225092621935b88c1ce68040/scipy/sparse/_compressed.py#L901
-    i, j, M, N = spmatrix._prepare_indices(i, j)
-    offsets = np.empty(n_samples, dtype=spmatrix.indices.dtype)
-    ret = csr_sample_offsets(
-        M, N, spmatrix.indptr, spmatrix.indices, n_samples, i, j, offsets
-    )
-    if ret == 1:
-        spmatrix.sum_duplicates()
-        csr_sample_offsets(
-            M, N, spmatrix.indptr, spmatrix.indices, n_samples, i, j, offsets
-        )
-    return offsets, (i, j, M, N)
-
-
 def _get_spmatrix_offsets_cupy(spmatrix, i, j):
     """Calculates the sparse matrix offsets for a set of rows ``i`` and columns ``j``."""
     # See _set_many() at
@@ -55,14 +35,16 @@ def _get_spmatrix_offsets_cupy(spmatrix, i, j):
 def _spmatrix_set_many(spmatrix, i, j, x):
     """spmatrix.__setitem__()"""
     if sp.issparse(spmatrix):
-        i, j = spmatrix._swap((i, j))
-        offsets, (i, j, M, N) = _get_spmatrix_offsets(spmatrix, i, j, len(x))
-    else:
-        i, j = spmatrix._swap(i, j)
-        offsets, (i, j, M, N) = _get_spmatrix_offsets_cupy(spmatrix, i, j)
+        spmatrix[i, j] = x
+        return
+
+    i, j = spmatrix._swap(i, j)
+    offsets, (i, j, M, N) = _get_spmatrix_offsets_cupy(spmatrix, i, j)
 
     mask = offsets > -1
+    # update where possible
     spmatrix.data[offsets[mask]] = x[mask]
+
     if not mask.all():
         # only insertions remain
         mask = ~mask