These are Steiner arborescense problems (directed Steiner problems) from a genetic context. For more information see JKCMAKSFB00 . The graphs in these instances are layered (only have forward arcs).The description of the file format is not jet finished. If you have any questions, please send an email.
The files can be found in the download section.
The column DC classifies the difficulty of the instance.
The letter after class gives an impression how long it takes to solve the problem using state-of-the-art soft- and hardware. secounds means less than a minute (this includes instances which can be solved in fractions of a second). minutes means less than an hour. hours is less than a day and days is less than a week. weeks mean it takes really a long time to solve this instance. ? means the instance is not solved or the time is not known.
If the number in the Opt column is written in italics the optimum is not known. The number given is the best know upper bound.