To enhance the performance of the Particle Swarm Optimization (PSO) algorithm, this paper proposes the following improvement strategies.
Firstly, a dual-population co-evolution framework based on Hooke’s Law competition mechanism is constructed, integrating the Differential Evolution (DE) algorithm with the PSO algorithm. Given that the two subpopulations have different optimization advantages, the algorithm fuses the search mechanisms of the two populations: the DE algorithm has a strong ability to maintain population diversity but converges slowly; while the PSO algorithm converges quickly but is prone to premature convergence, leading to a decrease in diversity. To integrate the advantages of both and compensate for their respective shortcomings, the algorithm designs an external archive based on Hooke’s Law competition mechanism to store candidate high-quality individual particles. The excellent particles in this archive are used to guide the update process of the DE population, thereby improving its convergence performance. Meanwhile, to prevent an extreme distribution of particles from the DE and PSO populations in the archive, a dynamic adjustment strategy is introduced to adaptively adjust the archiving ratio of the two types of particles within a preset range, maintaining the balance of the population structure and the efficiency of co-evolution.
Secondly, the iteration requires both early exploration and late exploitation capabilities. Therefore, an adaptive acceleration coefficient strategy based on experience tracing is adopted. Regular acceleration coefficients may lead to the neglect of certain new regions. This paper uses acceleration coefficients that conform to a Gaussian distribution, ensuring that the PSO algorithm can conduct effective searches based on reasonable experience in most cases, while occasionally exploring new regions to avoid premature convergence. During the algorithm’s evolution, the well-performing acceleration coefficients are saved in the archive. If the fitness does not improve for several consecutive iterations, the algorithm will trace historical successful experiences to guide its learning.
Finally, according to Equation (1), the evolution process of particles is influenced by parameters ω, c1, and c2. Therefore, time-varying control parameters are introduced during the algorithm’s iteration, and a perturbation based on the Sine improvement strategy is applied to the inertia weight ω in the later stage to effectively avoid falling into local optima. During the algorithm’s evolution, the well-performing inertia weights are saved in the archive. If the fitness does not improve for several consecutive iterations, the algorithm will trace the historical successful experiences of the inertia weight to guide its learning.
3.1. A Dual-Population Coevolutionary Framework Based on Hooke’s Law Competition Mechanism
In the early stage of algorithmic evolution, maintaining the diversity of particles is conducive to enhancing the global search capability of the algorithm, especially for complex multimodal optimization problems, where maintaining population diversity is particularly important. However, in the later stages of evolution, relying solely on diversity makes it difficult to achieve efficient convergence. Therefore, it is necessary to enhance the convergence speed while maintaining the global exploration capability. To this end, this paper proposes a dual-population hybrid particle swarm optimization algorithm framework based on Hooke’s law competition mechanism. By integrating the convergence efficiency of the particle swarm optimization algorithm (PSO) and the global search advantage of the differential evolution algorithm (DE), it achieves better search performance. This method divides the population into two subgroups: one subgroup originates from the DE algorithm, and the other subgroup originates from the PSO algorithm. The two subgroups coevolve through a designed information exchange mechanism, aiming to maintain population diversity while further improving the convergence speed. During the coevolution process, the algorithm adjusts the usage ratio of the two subgroups based on their fitness performance according to Hooke’s law: the subgroup with better performance will obtain a higher utilization rate, while the subgroup with poorer performance will have a corresponding reduction in its participation; at the same time, to avoid extreme phenomena, the adjustment of population utilization is limited within a reasonable range to ensure the stability and balance of the evolution.
The algorithm combines the DE algorithm with the particle swarm optimization algorithm (PSO). In the initial stage of the DE algorithm, the population initialization work needs to be completed first, and the key parameter configuration, including the scaling factor (F) and crossover rate (CR), etc., should be set. The algorithm gradually guides the population to converge to the optimal solution space by iteratively performing the three core operations of crossover, mutation, and selection.
The scaling factor
F (set to 0.5) and crossover rate
CR (set to 0.9) of the DE algorithm are referenced from the classic DE parameter configuration proposed by Zhang and Xie [
13], which has been verified to achieve a balanced performance between population diversity and convergence speed in multiple numerical optimization problems. This parameter setting is consistent with the standard configuration of DE-based hybrid algorithms in recent studies, ensuring the comparability and rationality of the experimental results.
(1) Mutation operation
As a key mechanism for algorithm innovation, the mutation operation generates new individuals with diversity by perturbing existing ones. A typical mutation strategy is shown in Equation (3), which breaks local optima by introducing randomness and provides the algorithm with the ability to explore new solution spaces:
where
F is generally within the range of [0.4, 1]. In this paper,
F is set to 0.5.
t represents the current iteration number. The size of the DE population is
ND.
r1,
r2, and
r3 are mutually exclusive integers within the range of [1,
ND].
However, the DE algorithm shows a relatively slow convergence speed. To enhance its convergence performance, using the particles that have performed better in history to guide the evolutionary process of the algorithm is an effective strategy. In this algorithm, the individuals that perform better during the evolutionary process are stored in an external archive, and the initial capacity of the archive is set to half of the population size. The update mechanism of the archive
used in the DE algorithm to store the superior evolutionary individuals is shown in Equation (4):
where
is the archive of the elite particles of the
t-th generation of DE,
ND is the population size of DE, and
represents the median fitness of the population in the
t-th generation of the Differential Evolution (DE) algorithm.
PSO has a relatively fast convergence speed, and the particles with excellent performance can effectively guide the evolution direction of the particle swarm. Therefore, the algorithm stores the particles with better performance in the archive, and these particles are called elite particles, while the rest are ordinary particles. The initial capacity of the archive is set to half of the population size of PSO, which is used to store the particles that perform well during the evolution process. The update mechanism of its
is shown in Equation (5):
where
is the elite particle archive of the
t-th generation of PSO,
NP is the population size of PSO, and
is the median fitness of the
t-th generation of the particle swarm optimization algorithm (PSO) population.
The elite particle archives of DE and PSO are combined to form the elite particle archive
DPR, as shown in Equation (6):
where
is the union of the elite particles of the
t-th generation of DE and PSO populations.
When mutating, a particle is randomly selected from the
DPR archive to guide the mutation of the particle, and the mutation equation is shown in Equation (7):
where
is a random particle in the union of the elite particles of the
t-th generation of DE and PSO,
F is the scaling factor, and
r1 and
r2 are mutually exclusive integers between [1,
ND].
(2) Crossover
The crossover operation fuses the components of the mutant vector with those of the original population individuals to generate the test vector. The crossover rate
CR effectively balances the diversity and convergence of the algorithm during the search process. The crossover equation is shown in Equation (8):
where
represents the component of the experimental vector of the
i-th particle in the
t-th generation in the
j-th dimension,
rm is a random number uniformly distributed in the interval [0, 1], and
jdim is an integer randomly selected from [1,
D]. The setting of
j =
jdim ensures that each individual undergoes crossover in at least one dimension, which can enhance the diversity of the population. The experimental vector
is generated by fusing the components of the mutation vector
and the target vector
. The crossover probability
CR determines the probability of selecting components from the mutation vector.
(3) Selection
Selection is a crucial step in genetic algorithms. Its core mechanism lies in comparing the fitness values of the target individual
and
, and retaining the individuals with better fitness values to enter the next generation population. The selection equation is shown in Equation (9):
where
is the new vector obtained by mutating Equation (8).
The standard Particle Swarm Optimization (PSO) algorithm is combined with the Differential Evolution (DE) algorithm. The algorithm acquires particles from the two populations of the Differential Evolution algorithm and the Particle Swarm Optimization algorithm respectively, achieving complementarity between the two algorithms. The particles in the Differential Evolution algorithm population can maintain the diversity of the algorithm, while the Particle Swarm Optimization algorithm can enhance the convergence speed of the algorithm. The component extracted from the Particle Swarm Optimization algorithm is
particle, with the control factor being
b1, and the other component is
extracted from the Differential Evolution algorithm, with the control factor being
b2.
b1 and
b2 are within the interval [0, 1], and their sum is 1.
b1 and
b2 are obtained from Equation (10):
where
bi (i = 1, 2) are the control factors, and
ri is a uniformly distributed random number in the interval (0, 1).
The differential algorithm and the particle swarm optimization algorithm are integrated. The new vector achieves complementary algorithmic characteristics by obtaining information samples from the two subpopulations. The new learning vector update Equation is shown in Equation (11):
where
is the learning vector of the
j-th dimension of the
i-th particle in the
t-th generation after the fusion of the differential algorithm and the particle swarm optimization algorithm,
is the learning vector of the
j-th dimension of the
i-th particle in the
t-th generation in the population of the particle swarm optimization algorithm,
is the learning vector of the
j-th dimension of the particle
i from the population of the differential algorithm in the
t-th generation,
b1 and
b2 are two random numbers distributed in the interval [0, 1], and their sum is 1. They are obtained by Equation (10).
The learning vector
is compared with the fitness value of the
i-th particle
. The one with the better fitness value is selected as the new learning vector
.
is given by Equation (12):
where
is given by Equation (11).
In the traditional PSO algorithm, all particles fly towards the global optimum, which easily leads to the loss of population diversity. In this algorithm, we divide the particles into elite particles and ordinary particles. Elite particles can boldly explore, while ordinary particles are not suitable for independently exploring the solution space. They can evolve under the guidance of elite particles. In this way of evolution, elite particles tend to move in the direction of their own historical optimum rather than the
Gbest direction, which enables the population to fly in more directions. Ordinary particles assist elite particles in local search by fusing the weighted center of elite particles, and the algorithm can achieve a balance between exploration and exploitation. The weighted center of elite particles is shown in Equation (13):
where
k represents the capacity of the elite particle archive, and
f(
) is the fitness of the
k-th particle.
The operations of the new learning vector, the weighted center of the elite particles, and the new DE population are as shown in Algorithm 1.
The dual-population co-evolution mechanism not only retains the fast convergence characteristic of PSO but also fully exploits the diversity advantage of the DE population. The size of the PSO elite archive and the DE elite archive is dynamically adjusted based on a competition mechanism of Hooke’s law. The size of the DE elite archive and the PSO elite archive competes for the elite particle archive size according to their performance. That is, if there are more particles with better fitness in the PSO population, the size of the PSO elite archive is increased; otherwise, it is decreased. Similarly, if there are more particles with better fitness in the DE population, the size of the DE elite archive is increased; otherwise, it is decreased. The increase ratio of both is limited to the interval [−0.1, 0.1].
| Algorithm 1 Module 1: PSO-DE Hybridization |
| Require: size(ND), F, CR, D, LB, UB, t, tmax |
| Ensure: |
| 1: Calculate the elite particle archive of DE by Equation (4) |
| 2: Calculate the elite particle archive of PSO by Equation (5) |
| 3: Union the elite particles from DE and PSO into by Equation (6). |
| 4: K = size(DPRᵗ) |
| 5: for i = 1 to ND do |
| 6: r1 ∈ [1, K]; r2, r3 ∈ [1, ND], r2 ≠ r3; |
| 7: |
| 8: for j = 1 to D do |
| 9: |
| 10: end for |
| 11: |
| 12: end for |
| 13: for i = 1 to NP do |
| 14: for j = 1 to D do |
| 15: |
| 16: |
| 17: |
| 18: end for |
| 19 end for: |
| 24: |
| return , Qk, |
In this paper, the linear mapping (i.e., linear transformation) method of interval values is adopted to map the input ratios inputmin and inputmax from the interval [0, 1] to the target ratio interval [−0.1, 0.1], with the corresponding output ratios being outputmin and outputmax. The new ratios obtained after mapping are used as the update ratios for the two elite populations.
To address the bottleneck in the differential evolution algorithm (DE) where the elite population update is prone to over-disturb the superior individuals, leading to an imbalance in the exploration-exploitation strategy, this paper adopts the generalized interval form of Hooke’s Law as a physical analogy mechanism, allowing the algorithm’s outstanding “elite population” to precisely adjust parameters within a reasonable range.
Hooke’s Law is a fundamental principle in elasticity mechanics, which essentially describes the linear relationship between the force (stress) and deformation (strain) of an elastic body within the elastic limit: the standard form is F = −kx (F is the elastic force, k is the stiffness coefficient, and x is the deformation). The generalized interval form limits this linear relationship within specific stress and strain intervals—mapping the normalized stress (input) to the force range of the elastic body. The expression is ε = kHooke⋅(σ − σ0), where σ is the normalized equivalent stress, corresponding to the effective force range of the elastic body (e.g., in this paper, σ ∈ [0, 1]); ε is the normalized equivalent strain within the elastic limit, corresponding to the effective deformation range of the elastic body (e.g., in this paper, ε ∈ [−0.1, 0.1]); kHooke is the coefficient of the interval mapping, which is used to convert the applied force into the corresponding deformation. (in this paper, kHooke is obtained from the interval boundaries as kHooke = (σmax − σmin)/(εmax − εmin) = outputmin − outputmax = 0.2).
In the algorithm, we analogize the “proportion score” (ranging from 0 to 1) of the best-performing group of particles (referred to as the “elite population”) to the “elastic stress” acting on these particles. Using the interval version of Hooke’s Law, this score is proportionally converted into a “mutation update ratio” (ranging from −0.1 to 0.1)—similar to the deformation of a spring under force. This ratio determines the extent to which the elite particles will be adjusted next. The proportional update of the DE elite population size is shown in Equation (14):
The proportional update of the PSO elite population size is shown in Equation (15).
where
- is the proportion of DE elite particles to be updated in the
t + 1 generation,
is the proportion of DE elite particles in the
t generation to all elite particles,
is the proportion of PSO elite particles to be updated in the
t + 1 generation,
is the proportion of PSO elite particles in the t generation to all elite particles,
outputmin is the minimum value of the proportion of elite particles to be updated,
outputmax is the maximum value of the proportion of elite particles to be updated,
inputmin is the minimum value of the proportion of elite particles, and
inputmax is the maximum value of the proportion of elite particles. The mapping coefficient is related to the Young’s modulus of the elastic body (characterizing the constraint characteristics of the mutation intensity), and the input midpoint (0.5) corresponds to the stress balance position (at this time, the mutation ratio is 0, and the proportion of elite individuals is directly retained unchanged).
During this process, the size of the DE elite population is denoted as NEDE, while the size of the PSO elite population is denoted as NEPSO. Based on experience, the update range for NEDE is set to [−0.1∙NEDE, 0.1∙NEDE], and for NEPSO, it is set to [−0.1∙NEPSO, 0.1∙NEPSO] each time.
The size of the subpopulations should be controlled within a reasonable range to prevent extreme population structures. In this paper, appropriate constraints are imposed on the sizes of the subpopulations of the Differential Evolution (DE) and Particle Swarm Optimization (PSO) algorithms. Specifically, the upper limit
NEmax and lower limit
NEmin of the subpopulation size are set to 40 and 10, respectively. The sizes of the PSO and DE subpopulations in the next generation are determined by Equations (16) and (17), respectively:
where
is the scale of the PSO elite particles to be updated in the (
t + 1)-th generation,
is the scale of the PSO elite particles in the
t-th generation,
is the update ratio of the PSO elite particles in the (
t + 1)-th generation,
is the scale of the DE elite particles to be updated in the (
t + 1)-th generation,
is the scale of the DE elite particles in the
t-th generation,
is the update ratio of the DE elite particles in the (
t + 1)-th generation, and
NEmax and
NEmin are the upper and lower limits of the subpopulation scale, respectively. The operation of the DE/PSO elite particle scale in the (
t + 1)-th generation is as shown in Algorithm 2.
| Algorithm 2 Module 2: Elite Population Size Adjustment based on Hooke’s Law |
| Require: , , , , NEmax = 40, NEmin = 10, NP, ND |
| Ensure: , |
| 1: calculate and |
| 2: |
| 3: |
| 4: |
| 5: = max(NEmin, min(NEmax, )) |
| 6: |
| 7: = max(NEmin, min(NEmax, )) |
| return , |
3.2. Adaptive Acceleration Coefficient Strategy Based on Gaussian Guidance and Empirical Traceability
From Equation (1), it can be seen that c1 and c2 are acceleration coefficients, where c1 represents the degree to which a particle is influenced by its own experience, and c2 represents the degree to which a particle is influenced by the group’s experience. Iteration requires early exploration ability and later exploitation ability. Therefore, in the early stage of iteration, a larger c1 and a smaller c2 should be set to enhance the diversity of the population. Conversely, in the later stage of evolution, a smaller c1 and a larger c2 should be adopted to accelerate the convergence speed of the algorithm. Thus, both c1 and c2 are linearly adjusted during the optimization process, with c1 increasing linearly and c2 decreasing linearly.
However, regular
c1 and
c2 may lead to the neglect of some new areas. This paper adopts the “concentration” principle in line with the Gaussian distribution to ensure that the Particle Swarm Optimization (PSO) algorithm can effectively search based on reasonable experience in most cases, thereby avoiding confusion in the search process; the “long tail” property of the Gaussian distribution ensures that PSO explores new areas with a small probability, avoiding premature convergence. Therefore, in HLCM-DHPSO, the definitions of
c1 and
c2 are respectively given by Equations (18) and (19):
where
iter and
itermax represent the current iteration number and the maximum number of iterations, respectively.
c1,init and
c1,final are the initial and final values of
c1, while
c2,init and
c2,final are the initial and final values of
c2. Ratnaweera et al. [
15] suggested that the value of
c1 should linearly decrease from 2.5 to 0.5, while
c2 should linearly increase from 0.5 to 2.5.
In the later stage of the algorithm’s evolution, the lack of particle diversity may lead to a slowdown in the evolution speed and getting stuck in a local optimum. At this point, appropriately adjusting the acceleration coefficients
c1 and
c2 can help the algorithm escape from the local optimum. During the evolution process, the
c1 and
c2 values that are beneficial to the algorithm’s improvement are saved in the
recordC file. The calculation Equations for the
c1 and
c2 files that are beneficial to the algorithm’s improvement are given by (20) and (21):
where
and
are the acceleration coefficients
c1 and
c2 of the (
j + 1)-th archived entry, and
f(
) is the fitness value of the
i-th particle in the
t-th generation.
The
recordc archive stores the
c1 and
c2 that are beneficial to the algorithm improvement, with a maximum storage capacity of
RN. The
recordc archive is shown in
Table 1.
When the number of
c1 and
c2 in the archive exceeds the limit, the records with poorer performance are eliminated based on the algorithm improvement rate. The algorithm improvement rate is as shown in Equation (22) and the acceleration coefficient at the position with the smallest
rk in
recordc is eliminated:
where
is the improvement rate of the
k-th record in the acceleration coefficient archive to the algorithm, and
RN is the archive size.
If the fitness does not improve in six consecutive iterations of the algorithm, the algorithm will trace back to the historical successful experience. From the perspective of stability, the algorithm traces back to the average of the previous experience. However, if only the historical experience is relied on for average calculation, the ordinary performance and excellent performance experiences will be treated equally, which may cause
c1 and
c2 to shift towards undesirable data, thereby reducing the search performance. To enhance the robustness of the algorithm, this study introduces a method for adaptively tracing back the acceleration coefficients
c1 and
c2 based on the algorithm’s improvement rate. The new acceleration coefficients
meanc1 and
meanc2 are updated according to Equations (23) and (24):
where
represents the improvement rate, which is given by Equation (22).
RN is the number of records in
recordc,
is the first acceleration coefficient
c1 of the
k-th record in
recordc, and
is the second acceleration coefficient
c2 of the
k-th record in
recordc. The operations of acceleration coefficients
c1 and
c2 are as shown in Algorithm 3.
| Algorithm 3 Module 3: Acceleration Coefficients Update |
| Require: iter, itermax, recordC, fcurr, fprev, stagnation, RN = 20 |
| Ensure: , |
| 1: (18) |
| 2: (19) |
| 3: if fcurr < fprev then |
| 4: (20) |
| 5: (21) |
| 6: (22) |
| 7: ] to recordC; trim to RN if oversized based on |
| 8: end if |
| 9: if stagnation ≥ 6 and recordC ≠ Ø then |
| 10: (23) |
| 11: (24) |
| 12: = meanc2 |
| 13: end if |
| 14: )) |
| return |
3.3. Sine-Improved and Experience Tracing-Based Adaptive Inertia Weight Strategy
During the iterative process, a larger inertia weight
ω is conducive to a thorough overall exploration of the global solution space, while a smaller inertia weight
ω is more beneficial for local fine exploitation. Therefore, in this paper, a linearly decreasing inertia weight strategy is adopted during the evolutionary process, and inspired by the Sine function, the Sine function is introduced to perturb the inertia weight to enhance the dynamic adjustment ability of the search process. The specific expression of the inertia weight
ω is shown in Equation (25):
where
ωi and
ωf represent the initial and maximum values of
ω respectively,
iter is the current iteration number, and
itermax is the maximum iteration number.
ωi is set to 0.9 and
ωf is set to 0.4.
The Sine function perturbation is applied when iter/itermax > 0.5. Specifically, the input of the Sine function is randomly sampled from the interval [0, π] using a uniform distribution (i.e., rand () × π, where rand () generates a random float in [0, 1]). This ensures a moderate and unbiased perturbation intensity to the inertia weight.
In the later stage of algorithm evolution, the lack of particle diversity may lead to a slowdown in the evolution speed and getting trapped in local optimal solutions. At this point, by appropriately adjusting the inertia weight
ω, the algorithm can be promoted to escape from local optima. During the evolution process, the
ω that is beneficial to the algorithm improvement is saved to the
recordω archive, and the calculation equation of the
ω archive that is beneficial to the algorithm improvement is given by Equation (26):
where
is the acceleration coefficient
ω of the (
j + 1)-th entry in the archive, and
f(
) is the fitness value of the
i-th particle in the
t-th generation.
The
recordω archive stores the inertia weights that are beneficial to the algorithm improvement, with a maximum storage capacity of
RN. The
recordω archive is shown in
Table 2.
When the number of ω in the archive exceeds the limit, the records with poorer performance are eliminated based on the algorithm improvement rate. The algorithm improvement rate is as shown in Equation (22), and the ω with the smallest in recordω is eliminated.
Similarly to the acceleration coefficient, if the fitness does not improve in six consecutive iterations, the algorithm will trace back to the historical successful experience. Considering the stability, the algorithm traces back to the mean of the previous experience. However, if only the historical experience is averaged, the ordinary and excellent experiences will be treated equally, which may cause
ω to shift towards undesirable data and thus reduce the search performance. To enhance the robustness of the algorithm, this study introduces a method for adaptively tracing back the inertia weight
ω based on the algorithm improvement rate. The new inertia weight
meanω is updated according to Equation (27).
From Equation (11), it can be seen that HLCM-DHPSO integrates the advantages of differential algorithm and particle swarm optimization algorithm in the optimization process, effectively balancing the diversity of particles and the convergence speed. The velocity update equation of the
i-th particle is shown in Equation (28). The position update equation of the particle is given by Equation (2):
where
represents the velocity of the
i-th particle in the
j-th dimension at the (
t + 1)-th generation.
represents the position of the
i-th particle in the
j-th dimension at the (
t + 1)-th generation.
i = {1, 2, 3, …,
NP}, where
NP is the size of the particle population.
ω is the inertia weight, given by Equations (25)–(27),
c1 and
c2 are the acceleration coefficients, given by Equations (18)–(24).
r1 and
r2 are two random numbers distributed between [0, 1],
is given by Equation (12),
represents the value of the
j-th dimension of the individual optimal position of the ith particle in the
t-th generation.
is given by Equation (13).
is given by Equation (5).
To sum up, the details of the dual-population hybrid particle swarm optimization algorithm based on Hooke’s law competition mechanism, HLCM-DHPSO, are shown in Algorithm 4.
| Algorithm 4 Main Algorithm: HLCM-DHPSO |
Require: NP = 50, ND = 50, D = 30, tmax = 1000, F = 0.5, CR = 0.5, NP = 100
|
| Ensure: gbest, fgbest |
| 1: Randomly initialize position vectors XPSO, XDE and velocity vectors v |
| 2: Calculate fitness f(XPSO) and f(XDE) for all individuals |
| 3: gbest = min([f(XPSO); f(XDE)]) |
| 4: NEPSO = ⌊NP/2⌋, NEDE = ⌊ND/2⌋ |
| 5: DPR = Top fPSO/DE of XPSO/DE based on Equations (4)–(6) |
| 6: recordC = Ø; stagnation = 0 |
| 7: for t = 1 to tmax do |
| 8: Calculate the value of inertia weight ωᵗ base on Equations (25)–(27) |
| 9: for i = 1 to NP do |
| 10: |
| 11: stagnation = |fcurr − fprev| < 10−8 ? stagnation + 1: 0 |
| 12: ] = MODULE3(t, tmax, recordC, fcurr, fprev, stagnation, RN) |
| 13: end for |
| 14: |
| 15: , 40, 10, NP, ND) |
| 16: |
| 17: , F, CR, D, LB, UB, t, tmax) |
| 18: for i = 1 to NP do |
| 19: based on Equation (28) and Equation (2), respectively; |
| 20: |
| 21: Update gbest |
| 22: end for |
| 24: end for |
| return gbest, fgbest |
3.4. Theoretical Analysis of HLCM-DHPSO
To justify the rationality of Hooke’s Law Competition Mechanism and the overall algorithm, this section provides a concise theoretical analysis focusing on convergence, stability, and its quantitative impact on exploration-exploitation balance, all based on the core velocity updated equation, Equation (28)
3.4.1. Convergence Analysis
The convergence of HLCM-DHPSO is guaranteed by two key properties derived from Equation (28).
- (1)
Boundedness of Velocity and Position
For both elite particles (
∈
) and ordinary particles (otherwise) in Equation (28). Inertia weight
ωt ∈ [0.4, 0.9] (
Section 3.3), acceleration coefficients
,
∈ [0.5, 2.5] (
Section 3.2), ensuring the weight of each update term is bounded.
Reference positions (, , ) are all within the search space [LB, UB], so the position differences (, etc.) are bounded by [LB, UB]. Thus, is bounded by vmax = 0.2 × (UB − LB) and remains within the search space.
- (2)
Monotonic Improvement of Fitness
In each iteration,
pbest and
gbest are only updated when a better fitness value is obtained, so the global fitness sequence
is non-increasing. By the Monotone Bounded Theorem,
converges to a limit value. Combined with the DE subpopulation’s global exploration (
Section 3.1) and Sine perturbation of inertia weight (
Section 3.3), the algorithm can escape local optima with non-zero probability, ensuring convergence to the global optimum.
3.4.2. Stability of Hooke’s Law Competition Mechanism
The HLCM-DHPSO maintains stable co-evolution of dual populations through two constraints
(1) Bounded Adjustment Ratio: The elite population size (NEPSO, NEDE) is adjusted within ±10% (Equations (16) and (17)), avoiding extreme sizes (e.g., NEDE < 10 or NEPSO > 40) that would disrupt exploration-exploitation balance.
(2) When the PSO and DE subpopulations perform equally well (
σ ∈ [0, 1],
Section 3.1), the adjustment ratio
ε =
kHooke (
σ − 0.5) = 0, meaning no adjustment is made. This equilibrium point prevents continuous oscillation of subpopulation sizes, ensuring stable co-evolution.
3.4.3. Quantitative Impact on Exploration-Exploitation Balance
The HLCM-DHPSO quantitatively regulates the balance by adjusting the elite population size, which directly correlates with exploration/exploitation intensity.
Let (proportion of PSO elite particles) and (proportion of DE elite particles). Since PSO excels at exploitation, exploitation intensity is positively correlated with PPSO, and Since DE excels at exploration, exploration intensity is positively correlated with PDE.
The HLCM-DHPSO adjusts and based on Equations based on Equations (14) and (15). If there is any change in the performance of PSO, and are updated by Equation (16) and (17) and vice versa. This quantitative adjustment ensures a dynamic balance between exploration and exploitation.
3.4.4. Computational Complexity Analysis
The computational complexity of HLCM-DHPSO is analyzed per iteration and compared with representative comparison algorithms (GGL-PSOD, SWFA, CRADE) to quantify its theoretical overhead. Let D be the problem dimension, Ntotal be the total population size (NPSO + NDE), and RN be the capacity of the experience-tracing archive (20 in this work).
(1) Per-iteration complexity of HLCM-DHPSO
The core operations include: (1) velocity and position update (Equation (28)) for dual populations: O (Ntotal∙D); (2) Hooke’s Law competition mechanism (elite size adjustment): O (Nelite) (negligible compared to Ntotal∙D); (3) experience-tracing for parameters: O (RN) (constant time). Thus, the total per-iteration complexity of HLCM-DHPSO is O (Ntotal∙D), which is the same asymptotic order as standard PSO, DE, and hybrid variants.
(2) Time Complexity Comparison of HLCM-DHPSO and Competitive Algorithms
The core complexity of the HLCM-DHPSO algorithm is O (Ntotal∙D), and its additional overhead is a constant O (RN + Nelite). The core complexity of the GGL-PSOD algorithm is O (N∙D), and its additional overhead is O (N) for ring topology update. The core complexity of the SWFA algorithm is O (N∙D), and its additional overhead is negligible due to the lightweight sliding window. The core complexity of the CRADE algorithm is O (N∙D), and its additional overhead is O (N∙D) for differential mutation of all individuals. It is proven that compared with its competitors, HLCM-DHPSO does not introduce an increased asymptotic complexity, and its additional cost is limited to constant-time auxiliary modules.