Refactor SimplexMeshBoundary function signature to use trailing return type

Author: Q-Minh

source/pbat/geometry/MeshBoundary.cpp

@@ -11,7 +11,7 @@
 namespace pbat {
 namespace geometry {
 
-std::tuple<IndexVectorX, IndexMatrixX> SimplexMeshBoundary(IndexMatrixX const& C, Index n)
+auto SimplexMeshBoundary(IndexMatrixX const& C, Index n) -> std::tuple<IndexVectorX, IndexMatrixX>
 {
     if (n < 0)
         n = C.maxCoeff() + 1;

source/pbat/geometry/MeshBoundary.h

@@ -27,8 +27,8 @@ namespace geometry {
  * @param n The number of vertices in the mesh. If -1, the number of vertices is computed from C.
  * @return A tuple containing the boundary vertices and the boundary facets
  */
-std::tuple<IndexVectorX, IndexMatrixX>
-SimplexMeshBoundary(IndexMatrixX const& C, Index n = Index(-1));
+auto SimplexMeshBoundary(IndexMatrixX const& C, Index n = Index(-1))
+    -> std::tuple<IndexVectorX, IndexMatrixX>;
 
 } // namespace geometry
 } // namespace pbat