Volume 2025, Issue 1 9699634
Research Article
Open Access

Inertial CQ Algorithm With Correction Terms for Split Feasibility Problems With Multiple Output Sets

Yang Liu

Yang Liu

East China University of Political Science and Law , Shanghai , China , ecupl.edu.cn

Search for more papers by this author
Yazheng Dang

Corresponding Author

Yazheng Dang

University of Shanghai for Science and Technology Business School , Shanghai , China

Search for more papers by this author
Kang Liu

Kang Liu

University of Shanghai for Science and Technology Business School , Shanghai , China

Search for more papers by this author
First published: 04 July 2025
Academic Editor: Chengming Huang

Abstract

We propose a new CQ algorithm which combines the inertial technique and correction terms for solving the split feasibility problem with multiple output sets in Hilbert spaces. Under suitable conditions, we prove the weak convergence. Moreover, we demonstrate the linear convergence when the split feasibility problem with multiple output sets satisfies some bounded linear regularity property. Finally, numerical experiments are conducted to demonstrate superiority of our method over related inertial CQ method and classical CQ method for the split feasibility problem with multiple output sets.

1. Introduction

Our objective in this paper is to propose a fast algorithm to solve the split feasibility problem with multiple output sets (SFPwMOS). Find an element x in real Hilbert spaces H and Hi, i = 1, ⋯, N such that
()
where C and Qi are nonempty, closed, and convex subsets of H and Hi, i = 1, ⋯, N, and Ai : HHi, i = 1, ⋯, N are nonzero bounded linear operators. When N = 1, the problem (SFPwMOS) will be the split feasibility problem (SFP):
()
The SFP was first introduced by authors in [1], which was widely studied by many authors over a long period of time. In recent years, many versions of CQ methods for solving the SFP (2) have been introduced and analyzed [27]. Byrne [2] introduced the first applicable and most celebrated method called the well-known CQ-algorithm:
()
where PC and PQ represent the metric projections onto C and Q, respectively, the step size λλ ∈ (0, 2/‖A2), and ‖A2 is the spectral radius of the matrix; ATA(AT denotes the adjoint operator of A).
In comparison to the basic algorithm, the algorithm incorporating inertial extrapolation steps have been demonstrated to achieve a faster convergence rate and require few iterations in theory and numerical experiments [813]. In [12], Dang et al. investigated CQ algorithms with inertial extrapolation steps.
()
and
()
where wk = xk + αk(xkxk−1), βk ∈ (0, 1), λ ∈ (0, 2/‖A2). Shehu and Gibali [13] proposed a new inertial relaxed method:
()
where , and γ > 0, l ∈ (0, 1), μ ∈ (0, 1), mk is the smallest non-negative integer . Moreover, inertial techniques have also achieved great success in real-world applications [1416].
The (SFPwMOS) problem has attracted a lot of scholars to analyze and study [1722]. Dang et al. [23] defined the function as follows:
()
It is not difficult to see that an element x is a solution of the SFPwMOS if and only if it is the solution of the following problem:
()
which is equivalent to
()
where NC(x) is the normal cone of C at point x. It implies that
()
where α is an arbitrary positive real number.
Due to the advantage of accelerating convergence, the application of inertial technology in solving SFPwMOS problems has become increasingly popular. Taddele et al. [24] introduced an extended inertial Halpern-type ball-relaxed CQ algorithm and proved a strong convergence of the sequence generated by the proposed algorithm under some mild assumptions. Okeke et al. [25] proposed two inertial accelerated algorithms which did not require prior knowledge of operator norm. Dang et al. [23] used a self-adaptive inertial viscosity projection algorithm (SIVP) for SFPwMOS:
()
where .
Inspired by the authors in [7, 11], in order to further enhance the convergence speed of the already studied CQ algorithms, we propose new inertial CQ algorithm correction terms for problem (1). Our main contributions of this paper are outlined as follows:
  • i.

    Our algorithm employs correction terms and self-adaptive step-size λk in each iterive step to improve the convergence

  • ii.

    Under some mild assumptions, we analyze the weak and linear convergence of the generated sequence

The rest of the paper is organized as follows: In Section 2, we present fundamental concepts and lemmas. Section 3 proposes an inertial CQ algorithm with correction terms for solving the SFPwMOS problem and shows its weak and linear convergence. In Section 4, we test the efficacy of the algorithm by two numerical experiments. Finally, some conclusions are given in Section 5.

2. Preliminaries

We recall some definitions and basic results that will be used in Section 3.

Suppose H is a real Hilbert space. We say that is
  • a.

    Nonexpansive if ‖TxTy‖≤‖xy‖, for all x, yH;

  • b.

    Firmly nonexpansive if for all x, yH.

Equivalently, ‖TxTy2 ≤ 〈xy, TxTy〉 for all x, yH.

From [26], T is firmly nonexpansive if and only if IT is firmly nonexpansive.

The operator PC is called the metric projection of H onto C; if given xH, there exists a unique point PC(x) ∈ C such that
()
We know from [27] that PC is a firmly nonexpansive mapping of H onto C. Furthermore,
()
and
()
Therefore,
()
A function is said to be convex if f(λx + (1 − λ)y) ≤ λf(x) + (1 − λ)f(y), ∀λ ∈ (0, 1), ∀x, yH. Also f is convex on H, and differentiable implies
()
We say that gH is a subgradient of at x provided
()
and f is lower semicontinuous (1sc) at x if yky implies f(y) ≤ lim infkf(yk) and f is lower semicontinuous on H if it is lower semicontinuous at every point yH.

Lemma 1. The following statements hold in:

  • i.

    for all x, yH;

  • ii.

    for all x, yH;

  • iii.

    .

3. Algorithm and Convergence

This section first introduces our inertial CQ algorithm with correction terms, then discusses its weak convergence and linear convergence rate.

Algorithm 1. Inertial CQ algorithm with correction terms.

Choose ρk ∈ (0, 4), αk ∈ [0, 1), δ ∈ [0, 1), w−2, w−1H, x−1, x0C. Set k≔0.
()
where .

Remark 1. Obviously, implies that . To ensure that λk is well-defined, we assume that ∇g(Wk) ≠ 0 in our convergence analysis.

3.1. Weak Convergence Analysis

To demonstrate the weak convergence and linear convergence rate, we need the following assumption and lemma.

Assumption 1. Throughout our convergence analysis, we assume that

  • a.

    0 <  lim inf ρk≤ limsup ρk < 4;

  • b.

    The solutions set S is nonempty.

Lemma 2. Both {wk} and {xk} generated by Algorithm 1 are bounded under Assumption 1.

Proof 1. For the rest of the convergence analysis of this paper, we define

()

From Algorithm 1, we have
()
Then, for any , that is, , we have
()
Consequently, since is firmly nonexpansive, from (14), we obtain
()
Therefore,
()
Now, from yk = xk + δ(wk−1xk), we obtain xk = (ykδwk−1/1 − δ) and ykwk−1 = (1 − δ)(xkwk−1). Then, from Lemma 1 (iii), we have
()
We furthermore obtain from (23) and (24) that
()
By Lemma 1 (iii), we obtain
()
Making use of (25) and (26), we obtain,
()
where
()
Applying (25) in (26), we obtain
()
Rearranging the above inequality, we obtain
()
Thus,
()
Therefore,
()
Define
()
Then, (33) becomes
()

Hence, βk ≥ 0 and βk+1βk since αk ∈ [0, 1) and δ ∈ [0, 1). Furthermore, we have from (34) that limkβk exists and {βk} is bounded. So, {yk} is bounded from (33).

Theorem 1. The sequence {xk} generated by Algorithm 1 converges weakly to a point in when Assumption 1 is satisfied.

Proof 2. Since {xk} is bounded from Lemma 2, we have that {xk} has at least one accumulation point vH. Suppose such that . We show that . Since C is a closed and convex subset of H, then C is weakly closed. Now, since and , it then follows that vC. To show that , we consider these two cases.

Case A: Assume that αk = 0 in (10). Then, our proposed algorithm reduces to
()
Hence, (33) becomes
()
from which we obtain that {xk} is bounded. We then obtain from (34) that
()
which implies (if δ ∈ (0, 1))
()
and
()
If δ = 0, k, then xk = yk and limk ‖xkyk‖ = limk ‖ykxk−1‖ = 0. We furthermore obtain from (34) that
()
Since , we have . Then,
()
Therefore, is bounded. From (40), we have . Since is bounded, there exists a subsequence {xk} of {xk}, ∀xkH1 which is weakly lower semicontinuous, and we have
()

Hence, AivQi, i.

Case B: Assume 0 < d1αkαk+1d2 < 1. Then, we have from (34) that (if ∈(0, 1))
()
Consequently, we have from (19) and (20) that
()
and
()
So, ‖wkxk‖ ≤ ‖wkyk‖ + ‖ykxk‖⟶0, k. Since {yk} is bounded, we have such that . Following a similar approach as in Case A, we have that . Now, suppose
()
Observe that
()
and
()
Therefore,
()
Hence,
()
Since limk ‖ykyk−1‖ = 0 and {xk} is bounded, we obtain and . By the existence of the limit of ak, we have from (50), limk ‖ykz‖ exists . Furthermore,
()
implies that limk ‖xkz‖ exists . We then conclude that {xk} converges weakly to a point in by Opial’s lemma [28].

Remark 2. We obtain boundedness and convergence of {xk} generated by Algorithm 1 using Assumption 1 without using the on-line rule: Choose αk such that and

()
where and α ≥ 0. The on-line rule (52) has been assumed severally by many authors whenever inertial CQ algorithm is studied (see, for example, [12, 22, 29, 30]). Consequently, the assumption “” is dispensed with in our Lemma 2 and Theorem 1.

3.2. Linear Convergence

In this subsection, we give the linear convergence rate of the sequences generated by Algorithm 1 under the following bounded linear regularity property of SFPwMOS:

For any r > 0 such that , where and is a closed metric ball, there exists γr > 0 such that
()
where dS(x)≔infySxy‖, xH. It was shown in [31] that if C and Qi are polyhedron, then SFPwMOS satisfies the bounded linear regularity property. For more details of sufficient conditions for the bounded linear regularity property, see ([31], Proposition 2.5).

Theorem 2. Let . Assuming that the SFPwMOS problem satisfies the bounded linear regularity property. {xk} generated by Algorithm 1 converges to a solution R-linearly when Assumption 1, αk = 0, δ = 0, ∀k ≥ 0, are fulfilled.

Proof 3. From (15), we have

()

By Lemma 2, we have that wk is bounded. Therefore, ∃r > 0 such that . Using the condition that SFPwMOS fulfills the bounded linear regularity property, it follows that ∃γr > 0 such that

()

We then obtain from (54) that

()
for each
()

We then obtain from (26) that ∀kk2,

()
if αk = 0,then (58) becomes (noting (10))
()

Thus, ∀kk2,

()
if and only if
()

Since 0 <  lim  inf ρk ≤ limsup ρk < 4, we obtain

()

Hence,

()

Consequently,

()

So, ∃k3k2 such that

()
if δ = 0 (36), then it becomes (noting (19))
()

Then, it is easy to see that {xk} converges linearly to z.

4. Numerical Experiment

In this section, we examine two numerical experiments to compare the effects of Algorithm 1, classic CQ in [2] and SIVP in [23]. All the codes are written in MATLAB and are performed with RAM 8 GB and Intel(R) Core (TM) i7-8265U CPU @ 1.60 GHz. We consider the following problems:

Example 1. Find a point x such that

()
where the sets C and Qi, i = 1, 2 and the linear bounded operators Ai, i = 1, 2 are defined as
()

In the experiments, we use Ekϵ as the stopping criteria, where EkTOLk,

()
where ϵ is a small enough positive number. Note that if Ek = 0, then xkS.

Firstly, for Algorithm 1 we take αk = 0.1, ρk = 3.0, δ = 0.1, w−1 = (0.2, 0.3, 0.5), w−2 = (0.3, 0.6, 0.9); in [23] for CQ, we take λk = 1, and in [23] for SIVP, we take λk = 1, tk = 0, ρk = 3.0 and αk = 0.1. The ϵ = 10−3, 10−4, 10−5, respectively. Then, we chose initial points x−1 = (0, 0.1, 0), x0 = (0, 0.1, 0) for Algorithm 1, SIVP and x0 = (0, 0.1, 0) for CQ to compare the experimental effects of the three groups. The behavior values of the function Ek with different ε are listed in Table 1, where “Iter.” and “Cpu” denote the number of iterations and cpu time in seconds.

We also plot Ek versus the number of iterative in Figure 1.

Obviously, from Table 1 and Figure 1, Algorithm 1 takes much less iterations and computing time than SIVP and CQ algorithm.

Secondly, select ρk = 3, δ = 0.1, w−1 = (0.2, 0.3, 0.5), w−2 = (0.3, 0.6, 0.9) for the same initial points x−1 = (0, 0.1, 0), x0 = (0, 0.1, 0), and we test the results for different αk and ε for Algorithm 1.

The behavior of the function Ek in Table 2 is described in Figure 2.

From Table 2 and Figure 2, we can see that as ε increases, the iteration steps decrease but when αk increases, the iteration steps still increase.

Table 1. The results of Algorithm 1 and SIVP and CQ algorithm for different ε.
ε 10−3 10−4 10−5
Algorithm 1 Inter. = 30 Cpu = 0.01 Inter. = 47 Cpu = 0.031 Inter. = 63 Cpu = 0.055
TOLk = 9.4237E − 04 TOLk = 8.8209E − 05 TOLk = 9.3113E − 06
  
SIVP Inter. = 45 Cpu = 0.012 Inter. = 65 Cpu = 0.042 Inter. = 85 Cpu = 0.072
TOLk = 9.5199E − 04 TOLk = 9.31750E − 05 TOLk = 9.3560E − 06
  
CQ Inter. = 77 Cpu = 0.16 Inter. = 111 Cpu = 0.052 Inter. = 146 Cpu = 0.096
TOLk = 9.6469E − 04 TOLk = 9.9749E − 05 TOLk = 9.8560E − 06
Details are in the caption following the image
Comparison with different ε for Algorithm 1 and CQ.
Table 2. The results of Algorithm 1 with different αk and ε.
ε αk = 0.2 αk = 0.5 αk = 0.9
10−3 Iter. = 33 Iter. = 42 Iter. = 54
TOL = 9.7664E − 04 TOL = 9.7212E − 04 TOL = 9.3819E − 04
  
10−4 Iter. = 51 Iter. = 65 Iter. = 82
TOL = 9.6424E − 05 TOL = 9.1123E − 05 TOL = 9.5076E − 05
Details are in the caption following the image
Comparison with different ε and ρk for Algorithm 1.

Example 2. Consider the following monotone inclusion problem [32]:

()
where and . Define the linear continuous operator L : L2([0, 2π])⟶L2([0, 2π]) as
()

The projection onto the set C can be computed as

()

The projection onto the set Q can be computed as

()

Let

()
be the stopping criterion. Table 3 and Figure 3 present the numbers of iterations needed by Algorithm 1 and SIVP (here, we do not consider the general CQ algorithm since it is no-inertial version). Set ρk = 3.0 for every k ≥ 0, δ = 0.9, λ = 1, tk = 0. Select inertial factors αk = 0.1, 0.3, 0.6, respectively. The specific results are shown in Table 3.

Figure 3 plots the trend of Ek with the iteration for αk = 0.1, 0.3, 0.6, with initial points (x0, x−1) = (t3, t3) for Algorithm 1 and SIVP, respectively.

Table 3 and Figure 3 also show that our algorithm performs better than SIVP.

Based on the above two numerical experiments, we can see that the application of the inertial technique and correction terms can improve the performance of the algorithm.

Table 3. Comparison of different inertial factors αk by Algorithm 1 and SIVP.
Iter. for Algorithm 1 Iter. for SIVP
x0 x−1 w−1 w−2 αk = 0.1 αk = 0.3 αk = 0.6 x0 x−1 αk = 0.1 αk = 0.3 αk = 0.6
t2 t t2/5 t2/5 16 18 21 t2 t 44 31 25
t2 t2 t2/5 t2/5 18 19 22 t2 t2 53 47 43
t3 t2 t2/5 t2/5 29 30 35 t3 t2 86 72 67
Details are in the caption following the image
Comparison of different αk by Algorithm 1 and SIVP.

5. Conclusions

In this paper, we propose an inertial CQ algorithm with correction terms for solving SFPwMOS. Under some suitable conditions, we show the weak convergence and linear convergence results by the bounded linear regularity property. Two numerical experiments show that our algorithm performs better than other algorithms.

Conflicts of Interest

The authors declare no conflicts of interest.

Author Contributions

Yang Liu, Yazheng Dang, and Kang Liu wrote the main manuscript text. All authors carried out all the experiments and reviewed the manuscript.

Funding

This work was supported by the National Key Research and Development Program of China (2023YFC3306100, 2023YFC3306105, 2023YFC3306103), Major Projects of the National Social Science Foundation (20&ZD199), Shanghai Philosophy and Social Science Planning Project (2023EFX011), National Natural Science Foundation of China under grants 72071130 and 71901145, and Humanities and Social Sciences Research Project of the Ministry of Education under grant 20YJC820030.

Data Availability Statement

The data used to support the findings of this study are included within the article.

    The full text of this article hosted at iucr.org is unavailable due to technical difficulties.