Hi there, congratulations for an excellent tool we have been using since 2006 for our research.
Generally, we use it for "just visualization", but sometimes we would need a better specification of the algorithms behind it.
We were using version 3.14.4 of the software and some small graphs present a four-level layout that has four independent sets in each layout, of different cardinality, in each layer (when we are using Hierarchical Layout - Optimal). The BFS option creates a layout of three layers but two of them are not independent sets.
In version 3.17.2 both layout options give the same layout, the one of BFS of the previous version.
We are interested to know more about the changes. We particularly enjoy the layout that has independent sets in each layer and we would like to know if there is a polynomial-time algorithm that creates these layouts, or any other formal detail that can allow us to understand the procedure in formal mathematical terms. The online information could not help to cover this gap.
In addition, we would like to know what may have happened between the two versions. If there was an optimal result before, why we are getting the BFS result now in the new version of the software.
We can facilitate to you some small graphs in case you need it, or if some debugging seems to be necessary to address the question.