The ChromaticNumber command which computes the chromatic number of a graph now uses a hybrid algorithm by default. This algorithm runs two separate implementations in parallel and returns the result of whichever method finishes first. Consequently, some examples which could not be solved in Maple 2017 in a reasonable amount of time can be quickly solved in Maple 2018. In the following example Maple 2017 is unable to determine the chromatic number after an hour of CPU time while Maple 2018 does so in seconds. The example is a random graph which appears in the paper "Optimization by Simulated Annealing: An Experimental Evaluation; Part II, Graph Coloring and Number Partitioning" by D. Johnson, C. Aragon, L. McGeoch, and C. Schevon.
memory used=266.60KiB, alloc change=10.94MiB, cpu time=48.00ms, real time=1.14s, gc time=0ns