The upper bound is the upper limit of constraint which the swarm must adhere to. This is used to update the swarm position and to scale it within range. 10 is the default value:
Please note that, depending upon the function you are optimizing, the upper and lower bounds could be quite different from the default. Consult the reference guide for your function and see what the upper and lower constraints are:
return Math.Max(Math.Min(OutPos, upperBoundDomain), lowerBoundDomain);
Upper Bound = 10:
3D Plot
Upper Bound = 20:
3D Plot