This function takes a branch `igraph` as object and a starting `vertex` as object, finds the longest path that starts from that vertex.
make_idline(branch, vert_rank)
| branch | an `igraph` object storing data for a panicle branch. |
|---|---|
| vert_rank | a number indicating the `rank` attribute that identifies the staring vertex. |
The longest path is assumend to be the main branch axis
This function returns a character vector that stores `type` of the vertexes (Secondary, Spikelet, etc.) along that axis ordered from the starting vertex (supplied in `vert_rank`) going outward.