Update main.py

try proposed fix according to StatBiomed#25 (comment)

spatialdm/main.py

@@ -38,7 +38,14 @@ def _Euclidean_to_RBF(X, l, singlecell=single_cell):
 
         # At single-cell resolution, no within-spot communications
         if singlecell:
-            np.fill_diagonal(rbf_d, 0)
+            # Convert csr_matrix to lil_matrix for efficient row operations
+            rbf_d_lil = rbf_d.tolil()
+
+            # Set diagonal elements to zero
+            rbf_d_lil.setdiag(0)
+
+            # Convert back to csr_matrix if needed
+            rbf_d = rbf_d_lil.tocsr()
         else:
             rbf_d.setdiag(np.exp(-X.diagonal()**2 / (2 * l ** 2)))