(fix) handle empty case in get_matrix

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "scikit_build_core.build"
 
 [project]
 name = "chalc"
-version = "6.0.0"
+version = "6.0.1"
 authors = [{ name = "Abhinav Natarajan", email = "[email protected]" }]
 description = "Persistent homology of chromatic Delaunay filtrations"
 readme = { file = "README.md", content-type = "text/markdown" }

src/chalc/sixpack.py

@@ -467,7 +467,11 @@ def get_matrix(self, diagram_name, dim=None):
 				simplices.add(d)
 			for s in dgm._unpaired:
 				simplices.add(s)
-			dim = list(range(max(np.array(self._dimensions)[list(simplices)])))
+			relevant_dims = np.array(self._dimensions)[list(simplices)]
+			if not relevant_dims:
+				# there are no features in the diagram
+				return []
+			dim = list(range(max(relevant_dims)))
 		if isinstance(dim, int):
 			# a p-dimensional homology class is captured by a pairing of (p+1) simplices for kernels
 			if diagram_name == "ker":