# Forced colorings with IGraph/M

Is it possible to force the colors of certain vertices in a graph so that the function which finds a minimum coloring will then extend the partial coloring with the fewest possible number of extra colors, without recoloring what has already been colored? If I understand the documentation of IGraph/M correctly, this is not quite possible, but maybe I am wrong. Am I correct in saying that the "ForcedColoring" option doesn’t quite allow this? Is there any other way to do this or otherwise hijack the IGMinimumVertexColoring function? This would be a great option if it were to be implemented, this is a frequent situation in coloring graphs, especially when you know something about the structure of your graph which allows you to quickly color part of it, having only a small part of the graph left to color with a minimum number of extra colors.

• I think the right place for IGraphM feature requests is here. Jun 25 '19 at 18:28
• Thanks for the pointer. I would like to leave the question, in case someone knows a way to do this, in any way ... or if you suggest to delete, then maybe I will, please do say
– EGME
Jun 25 '19 at 18:29
• @JasonB. Right, thanks as I said. Apparently, I don’t have access to that site (nor will creating an account work :( ...
– EGME
Jun 25 '19 at 18:34
• @EGME you can definitely add a feature request. Make a GitHub account, login, go here: github.com/szhorvat/IGraphM/issues/new and write your request. The project is public and open on GitHub so anyone can leave a comment Jun 25 '19 at 18:41
• @b3m2a1 Thanks, maybe I will try later, perhaps there is something wrong with my connection at the moment ...
– EGME
Jun 25 '19 at 18:42

What you are asking for is not implemented in IGraph/M at the moment. You are correct that the "ForcedColoring" option doesn't quite do this at the moment. What it does is that it forces different colours on a set of vertices, but it is not currently possible to specify what those colours should be.

However, it is a reasonable request that is not too hard to implement. I will try to include this in the next release—but no promises (I'm very busy at the moment).

As others said, the correct place for feature requests is the issue tracker. Please do open an issue to make sure I won't forget about.

• Thanks ... I will try opening an issue ... I had trouble signing up ... hopefully tomorrow
– EGME
Jun 25 '19 at 19:45
• If you cannot, ping me here and I'll create the issue myself. However, it would be better if you could create an account so that we can continue the discussion in the issue tracker. Jun 25 '19 at 19:47
• Ok, I will try ... I don’t know what is the issue ... but will try .. by the way, what is “to ping” ? Sorry, not flowing with the times ...
– EGME
Jun 25 '19 at 19:48
• Just comment on this post so that I get a notification. You can write my name with an "at" character like this: @EGME Then I get a notification, provided that I commented in the same thread before. Jun 25 '19 at 19:50
• ok, thanks ... and will try the issue tracker tomorrow
– EGME
Jun 25 '19 at 19:51