• The probabilistic function, P
k
ij(t) , is designed to favour the selection of a
road that has a high pheromone value, tÝ , and high visibility value, ?Ý , which is given
by, l/d
ij, where d
ij is the distance to the city. The pheromone scaling factor, a“ ,
and visibility scaling factor, ßG , are parameters used to tune the relative
importance of pheromone and road length in selecting the next city.
Apply Local Search
• Not used in Ant System, but is used in several variations of the TSP problem
where 2-opt or 3-opt local optimizers are used.
Best Tour check
• For each ant, calculate the length of the ant’s tour and compare to the best
tour’s length. If there is an improvement, update it.
Update Trails
• Evaporate a fixed proportion of the pheromone on each road.
• For each ant perform the “ant-cycle” pheromone update.
• Reinforce the best tour with a set number of “elitist ants” performing the “antcycle”
pheromone update.
• The probabilistic function, Pkij(t) , is designed to favour the selection of aroad that has a high pheromone value, tÝ , and high visibility value, ?Ý , which is givenby, l/dij, where dij is the distance to the city. The pheromone scaling factor, a“ ,and visibility scaling factor, ßG , are parameters used to tune the relativeimportance of pheromone and road length in selecting the next city.Apply Local Search• Not used in Ant System, but is used in several variations of the TSP problemwhere 2-opt or 3-opt local optimizers are used.Best Tour check• For each ant, calculate the length of the ant’s tour and compare to the besttour’s length. If there is an improvement, update it.Update Trails• Evaporate a fixed proportion of the pheromone on each road.• For each ant perform the “ant-cycle” pheromone update.• Reinforce the best tour with a set number of “elitist ants” performing the “antcycle”pheromone update.
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