c1, c2	personal cognition coefficient, social cognition coefficient
c1max, c2max	maximum values of acceleration coefficients
c1min, c2min	minimum values of acceleration coefficients
D	optimal route length
i	i-th particle
K	evaluation parameter
M	maximum number of iterations
m	current number of iterations
mcri	critical number of iterations
N	number of particles
P	number of successfully converged particles in a single iteration
Pis	individual best known position
Pgs	swarm best known position
Q	number of planned points
r1, r2	random numbers
R	swarm size
s	s-th dimension
vis	velocity value for s-th dimension and i-th particle
Vi	velocity vector
w	inertia weight
wmax, wmin	maximum and minimum value of inertia weight
Xi	position vector
xis	position value for s-th dimension and i-th particle
Abbreviations
ACO	ant colony optimization
APSO	particle swarm optimization with adaptively controlled acceleration coefficients
AWIPSO	particle swarm optimization with adaptively controlled acceleration coefficients, linearly descending inertia weight, and random grouping inversion
AWPSO	particle swarm optimization with adaptively controlled acceleration coefficients and linearly descending inertia weight
CPSO	conventional particle swarm optimization
NGC	navigation, guidance and control system
PSO	particle swam optimization
TSP	traveling salesman problem
USV	unmanned surface vehicle