message: Added note regarding returning a PCA basis subset
diff: @@ -206,6 +206,8 @@ public:
  * vectors, but only the block that is relevant for the vertex \p vertex_id.
  *
  * Todo: Can we return a const & view that points into the original data?
  + * I think actually .block returns a const, and by not defining our function
  + * const, we might copy the data here actually?
  *
  * @param[in] vertex_id A vertex index. Make sure it is valid.
  * @return A 1x3? 3x1? matrix that points to the rows in the original basis.
  