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Solutions of linear control systems on Lie groups

  • Victor Ayala EMAIL logo , Alexandre J. Santana , Simão N. Stelmastchuk and Marcos A. Verdi
Published/Copyright: December 31, 2024

Abstract

An explicit solution for linear control systems on Lie groups is presented using the variation of parameters method. This solution is formulated as a series of Lie brackets, and the convergence of these series is analyzed. Additionally, a concept of equivalence between two elements within this class is introduced.

MSC 2010: 93C05; 34A05; 37C15

1 Introduction

The main purpose of this study is to explicitly establish the solution of linear control systems on Lie groups. While this class of control systems has been studied since the 1980s, the number of papers addressing this concept has recently increased significantly (see Ayala et al. [1], Da Silva et al. [2,3] and the references therein). In [4], Ayala and Kizil studied the solutions of linear control systems, leveraging that, in this context, the solution evaluated in a point g of a Lie group is given by the product of the solution at the identity by the drift flow at g . However, this work takes a different approach by presenting a computable solution using the method of variation of parameters. To the best knowledge available, this type of solution for linear systems has not yet been documented in the literature. To define linear control systems, consider G a real finite-dimensional and connected Lie group with Lie algebra g (set of right invariant vector fields on G ). Denoting by e the identity of G , a vector field X on G is called linear if for all Y g , [ X , Y ] g and X ( e ) = 0 . A linear control system or a linear system on G is given by

(1) g = X ( g ) + i = 1 l u i Y i ( g ) ,

where the drift X is a linear vector field on G , the vector fields Y 1 , Y 2 , , Y l are right invariant on G and u = ( u 1 , , u l ) are the input maps such that u i : R R are piecewise constant functions.

To describe the explicit solution of system (1), the work of Magnus [5] is considered, which provides the solution of a differential equation

g = A ( t ) g ,

on Lie groups G . Magnus presents the solution in the form of a series, applicable in a general context (see Theorem III in [5]). In the following decades, some authors established sufficient conditions for the convergence of this series (see Theorem 2.9 in the study by Iserles and Nooorsett [6] and Theorem 3 of Moan-Niesen [7]). In this context, to obtain the solution to (1), the variation-of-parameters method is used, combined with the results of [5]. Consequently, the solution is expressed as a series, and we proceed to investigate the convergence of this series.

This article is organized as follows: In Section 2, the solution to system (1) is established, along with a discussion of its convergence within nilpotent Lie groups and matrix Lie groups. In addition, an example in low dimension is provided. Section 3 examines the equivalence of systems using Magnus’s series, demonstrating that this equivalence preserves the reachable sets of control systems.

2 Solution of linear system on Lie group

The main outcome of this section is Theorem 1, which clearly establishes the solution for the system described in equation (1). In addition, a low-dimensional example is presented, along with an examination of the conditions for the convergence of this solution in the context of matrix Lie groups. To accomplish this, we first considered the following differential equation on G :

(2) g = A ( t ) g ,

where the real integrable matrix A ( t ) represents a curve in the Lie algebra g = T e G , A ( t ) g = d ( R g ) e ( A ( t ) ) , and R g standing for the right translation. The solution of equation (2) (see Theorem III in [5]) reads as follows:

(3) g ( t ) = e x p Ω ( t ) ,

where

Ω ( t ) = 0 t A ( s ) d s 1 2 0 t 0 s A ( r ) d r , A ( s ) d s + 1 4 0 t 0 s 0 r A ( σ ) d σ , A ( r ) d r , A ( s ) d s

Denote by ϕ t the flow of the linear vector field X . Solutions of (1) are sought in the form g ( t ) = ϕ t ( c ( t , u ) ) , where c ( t , u ) G for fixed u . To enhance clarity in the discussion, using the notation c ( t ) is advisable. Therefore,

(4) g ( t ) = X ( ϕ t ( c ( t ) ) ) + ( d ϕ t ) c ( t ) ( c ( t ) ) .

Comparing (1) and (4), we have that c ( t ) satisfies

(5) i = 1 l u i ( t ) Y i ( ϕ t ( c ( t ) ) ) = ( d ϕ t ) c ( t ) ( c ( t ) ) .

Now, take b ( t ) = c ( t ) c ( t ) 1 , where this product is ( d R c ( t ) 1 ) c ( t ) ( c ( t ) ) . Then

(6) ( ( d R c ( t ) 1 ) c ( t ) ) 1 b ( t ) = c ( t ) ,

and thus,

( d R c ( t ) ) e ( b ( t ) ) = c ( t ) .

Therefore, we obtain the following equation:

(7) c ( t ) = b ( t ) c ( t ) .

Now, by (3), the solution of (7) is

(8) c ( t ) = e x p C ( t ) ,

where

C ( t ) = 0 t b ( s ) d s 1 2 0 t 0 s b ( r ) d r , b ( s ) d s + 1 4 0 t 0 s 0 r b ( σ ) d σ , b ( r ) d r , b ( s ) d s

Let D be the derivation associated with X , specifically the derivation of g such that D = a d ( X ) (see Section 3 of [8] for more details). Note that using (4) and (6), we have

(9) ( d ϕ t ) c ( t ) ( c ( t ) ) = ( d ϕ t ) c ( t ) ( ( d R c ( t ) ) e ( b ( t ) ) ) = ( d ( ϕ t R c ( t ) ) ) e ( b ( t ) ) .

Because X is a linear field, its flow ϕ t : G G is a homomorphism of G . Thus,

ϕ t R c ( t ) = R ϕ t ( c ( t ) ) ϕ t .

Consequently, recognizing that ϕ t ( c ( t ) ) = g ( t ) , we have that the last term of (9) becomes

(10) ( d ( R g ( t ) ϕ t ) ) e ( b ( t ) ) = ( d R g ( t ) ) e ( d ϕ t ) e ( b ( t ) ) .

By combining (5), (9), and (10), we obtain

i = 1 l u i ( t ) Y i ( ϕ t ( c ( t ) ) ) = ( d R g ( t ) ) e ( d ϕ t ) e ( b ( t ) ) .

It follows that

( d ϕ t ) e ( b ( t ) ) = ( ( d R g ( t ) ) e ) 1 ( i = 1 l u i ( t ) Y i ( g ( t ) ) ) = i = 1 l u i ( t ) ( ( d R g ( t ) ) e ) 1 ( Y i ( g ( t ) ) ) .

Denoting Y i ( e ) by Y i and considering that these vector fields are right invariant, the last equality becomes

(11) ( d ϕ t ) e ( b ( t ) ) = i = 1 l u i ( t ) Y i .

Knowing that ( d ϕ t ) e = e t D and based on equation (11), it follows that

b ( t ) = e t D i = 1 l u i ( t ) Y i = i = 1 l u i ( t ) e t D Y i .

Then

(12) C ( t , u ) = 0 t i = 1 l u i ( s ) e s D Y i d s + 1 2 0 t 0 s i = 1 l u i ( r ) e r D Y i d r , i = 1 l u i ( s ) e s D Y i d s + 1 4 0 t 0 s 0 r i = 1 l u i ( σ ) e σ D Y i d σ , i = 1 l u i ( r ) e r D Y i d r , i = 1 l u i ( s ) e s D Y i d s

Finally, the solution of system (1) is

g ( t , u , e ) = ϕ t ( c ( t ) ) = ϕ t ( e x p C ( t , u ) ) = e x p ( e t D C ( t , u ) ) .

To summarize, suppose that G satisfies the convergence condition given by Magnus, that is, 0 t A ( τ ) 2 d τ < π (see Theorem 3 in [7]). Then, considering the series C ( t , u ) , we can state the following theorem.

Theorem 1

Let G be a connected Lie group. Assume the aforementioned convergence condition. Then the solution g ( t , u , e ) of system (1), with the initial condition g ( 0 , u , e ) = e , is given by

g ( t , u , e ) = e x p ( e t D C ( t , u ) ) .

Corollary 2

Under the assumption of Theorem 1, the solution g ( t , u , x ) of system (1), with initial condition g ( 0 , u , x 0 ) = x 0 , is given by

g ( t , u , x ) = e x p ( e t D C ( t , u ) ) ϕ t ( x ) .

Example 3

Take the Heisenberg group given by the set of matrices of the form

1 x z 0 1 y 0 1 1 ,

where x , y , z R . Its Lie algebra g can be identified with R 3 , where the bracket is given by

[ ( x 1 , y 1 , z 1 ) , ( x 2 , y 2 , z 2 ) ] = ( 0 , 0 , x 1 y 2 x 2 y 1 ) .

Take a basis { X , Y , Z } of g such that [ X , Y ] = Z and the other brackets are zero. A straightfoward computation shows that the linear vector fields on G can be written as follows:

X = ( a x + d y ) x + ( b x + e y ) y + ( 1 2 ( b x 2 + d y 2 ) + c x + f y + ( a + e ) z ) z ,

and the associated derivation D = a d ( X ) is

(13) D = a d 0 b e 0 c f a + e .

Since brackets involving three or more elements are null, it turns out that the solution g ( t , u ) of the system

g = X ( g ) + u ( t ) Y ( g )

is given by

g ( t , u ) = exp e t D 0 t u ( s ) e s D Y d s 1 2 0 t 0 s u ( r ) e r D Y d r , u ( s ) e s D Y d s .

In the remainder of this section, we discuss the convergence of series C ( t , u ) . In the case of nilpotent Lie groups, we have C ( t , u ) converges for every t > 0 .

Our next step is to show the condition of convergence in the case of matrix Lie groups. If G is a matrix group and 0 t A ( τ ) d τ < π , then the Magnus series converges, and its sum C ( t , u ) satisfies exp ( C ( t , u ) ) = c ( t ) [7].

In our context, we have that A ( t ) = b ( t ) = i = 0 m u i ( t ) e t D Y i . Moreover, assume that G semisimple, we have that D = ad ( X ) for some X g , then

A ( τ ) i = 1 l u i ( t ) e t D Y i i = 1 l u i ( t ) e t ad ( X ) Y i i = 1 l u i ( t ) ad ( e t ) X Y i .

Suppose that the norm is given by the Cartan Killing metric. Then, by Ad -invariance, we obtain

A ( τ ) i = 1 l u i ( t ) Y i .

Now considering that the control maps are bounded, one can take the norm given by u i = sup { u i ( t ) : t R } . Since

0 t A ( τ ) d τ i = 1 l 0 t u i ( t ) Y 1 d τ t i = 1 l u i Y i ,

we obtain the following condition: if

t < π i = 1 l u i Y i ,

then 0 t A ( τ ) d τ π , ending the proof.

Proposition 4

Let G be a matrix Lie group with an Ad-invariant metric. Then, for a bounded control u, the series C ( t , u ) converges if

t < π i = 1 l u i Y i .

As a consequence of Theorem 2.9 [6], we have the next proposition.

Proposition 5

With the same assumptions as in the previous proposition, suppose there exists a t > 0 such that the control u is bounded by t λ in [ 0 , t ] . Then C ( t , u ) converges if

0 t min t , λ + 1 8 i = 0 l Y i 1 ( λ + 1 ) .

Furthermore, t does not depend on the derivation D.

A convergence condition can now be established based on the derivation, specifically the largest eigenvalue of that derivation. In fact, it is important to note that

A ( τ ) i = 1 l u i ( t ) e t D Y i i = 1 l u i ( t ) e t D Y i i = 1 l u i ( t ) e t D Y i i = 1 l u i ( t ) e t α Y i i = 1 l u i ( t ) e t α max { Y i } ,

where α is the largest eigenvalue of D . Then,

0 t A ( τ ) d τ 0 t i = 1 l u i ( τ ) e τ α max { Y i } d τ 0 t i = 1 l u i e τ α max { Y i } d τ = i = 1 l u i max { Y i } 0 t e τ α d τ = i = 1 l u i max { Y i } e t α 1 α = max { Y i } e t α 1 α i = 1 l u i .

Moreover,

max { Y i } e t α 1 α i = 1 l u i < π e t α < α π max { Y i } i = 1 l u i + 1 t < 1 α ln α π max { Y i } i = 1 l u i + 1 .

Thus, the following result has been established.

Proposition 6

Suppose u is a bounded admissible control. Then, for

t < 1 α ln α π max { Y i } i = 1 l u i + 1 ,

the series C ( t , u ) converges.

3 Equivalence of linear systems

This section discusses the equivalence of linear control systems using the previous series C ( t , u ) and demonstrates that this equivalence preserves the reachable sets. This equivalence is given by a conjugation of the systems flows, and hence, we first note that in general, the topological conjugation of two flows is given by a homeomorphism between the state spaces of the flows. However, because the continuous isomorphism of Lie groups is differentiable, we consider conjugation by differentiable isomorphisms. Consider the following two linear systems on G

(14) g = X ( g ) + i = 1 l u i ( t ) X i ( g ) ,

(15) h = Y ( h ) + i = 1 l u i ( t ) Y i ( h ) .

We denote by ϕ t and ψ t the flows of X and Y , and by D X and D Y their derivations, respectively. Suppose that there exists a differentiable homomorphism H : G G such that

  1. H ϕ t = ψ t H ;

  2. ( d H ) e X i ( e ) = Y i ( h ( e ) ) for every i = 1 , , n .

The following equivalences can be established.

Proposition 7

Let H : G G be a differentiable homomorphism.

The following sentences are equivalent:

(i) H ϕ t = ψ t H ;

(ii) ( d H ) ϕ t ( g ) ( X ( ϕ t ( g ) ) ) = Y ( ψ t ( H ( g ) ) ) ;

(iii) ( d H ) e ( e t D X X ) = e t D Y ( d H ) e ( X ) ;

(iv) ( d H ) e ( D X ) = D Y ( d H ) e ( X ) .

Proof

First, suppose H ϕ t = ψ t H , then

( d H ) ϕ t ( g ) d d t ( ϕ t ( g ) ) = d d t ( ψ t H ( g ) ) ,

hence it follows (ii) ( d H ) ϕ t ( g ) X ( g ) = Y ( H ( g ) ) . The uniqueness of solutions to differential equations is used to deduce (i) from (ii).

Now, consider (i), take the derivative at e on both sides of this equation and use the fact that ( d ϕ t ) e = e t D X to obtain (iii).

Now, assuming (iii), d ( H ϕ t ) e = d ( ψ t H ) e . Since G is connected, (i) holds.

It is clear that equality (iii) implies (iv). To obtain (iii) from (iv), it is sufficient to write e t D X as a power series and apply ( d H ) e .□

Lemma 8

Suppose that there exists a homomorphism H : G G such that (A) and (B) hold. Denote by C 1 ( t , u ) and C 2 ( t , u ) the series given in (12) corresponding to the linear control systems (14) and (15), respectively. Then, ( d H ) e ( C 1 ( t ) ) = C 2 ( t ) .

Proof

Observe that C 1 ( t ) and C 2 ( t ) satisfy the differential equations

d C 1 ( t ) d t = k = 0 B k k ! a d C 1 k ( γ ( t ) ) and d C 2 ( t ) d t = k = 0 B k k ! a d C 2 k ( δ ( t ) ) ,

where B k denotes the Bernoulli numbers,

γ ( t ) = i = 1 l u i ( t ) e t D X X i and δ ( t ) = i = 1 l u i ( t ) e t D Y Y i .

From the aforementioned proposition, it follows that ( d H ) e ( γ ( t ) ) = δ ( t ) . Furthermore, because ( d H ) is an isomorphism of the Lie algebras, we have

d d t ( ( d H ) e ( C 1 ( t ) ) ) = ( d H ) e k = 0 B k k ! a d C 1 k ( γ ( t ) ) = k = 0 B k k ! a d ( d H ) e ( C 1 ) k ( δ ( t ) ) .

Then, ( d H ) e ( C 1 ( t ) ) and C 2 ( t ) satisfy the same differential equation with initial condition ( d H ) e ( C 1 ( 0 ) ) = 0 = C 2 ( 0 ) . Therefore, ( d H ) e ( C 1 ( t ) ) = C 2 ( t ) .□

Theorem 9

Let H : G G be a homomorphism of Lie groups. The solutions of (14) and (15) are denoted by f ( t , u ) and g ( t , u ) , respectively. Therefore, the following conditions are equivalent:

  1. H ( g ( t , u ) ) = f ( t , u ) ;

  2. H ϕ t = ψ t H and ( d H ) e X i ( e ) = Y i ( H ( e ) ) for every i = 1 , , n .

Proof

Suppose that the second condition holds. From Theorem 1, the solutions of linear systems (14) and (15) are as follows:

g ( t , u ) = exp ( e t D X C 1 ( t ) ) and f ( t , u ) = exp ( e t D Y C 2 ( t ) ) ,

where C 1 ( t ) and C 2 ( t ) are given in (12). Then

H ( g ( t , u ) ) = H ( exp ( e t D X C 1 ( t ) ) ) = exp ( ( d H ) e e t D X C 1 ( t ) ) .

From Proposition 7, we have H ( g ( t , u ) ) = exp ( e t D Y ( d H ) e C 1 ( t ) ) , then by Lemma 8, we obtain condition (1). Now suppose that H ( g ( t , u ) ) = f ( t , u ) . Then,

(16) ( d H ) g ( t , u ) X ( g ( t , u ) ) + i = 1 l u i ( t ) X i ( g ( t , u ) ) = Y ( f ( t , u ) ) + i = 1 l u i ( t ) Y i ( f ( t , u ) ) .

Taking t = 0 , it follows that

( d H ) e X ( e ) + i = 1 l u i ( t ) X i ( e ) = Y ( e ) + i = 1 l u i ( t ) Y j ( e ) ,

since g ( 0 , u ) = f ( 0 , u ) = e . As X and Y are linear vector fields, we have

i = 1 l u i ( 0 ) [ ( d H ) e ( X i ( e ) ) Y i ( e ) ] = 0 .

Knowing that the aforementioned equality holds for all control u ( t ) = ( u 1 ( t ) , , u n ( t ) ) , we conclude that

(17) ( d H ) e ( X i ( e ) ) Y i ( e ) = 0 .

It means that ( d H ) e ( X i ( e ) ) = Y i ( e ) , for every i = 1 , , n .

On other hand, we can write equation (16) as follows:

( d H ) g ( t , u ) X ( g ( t , u ) ) Y ( f ( t , u ) ) = i = 1 l u i ( t ) [ ( d H ) e ( X i ( g ( t , u ) ) ) Y j ( f ( t , u ) ) ] .

By utilizing the right invariance of vector fields and knowing that H is a homomorphism, we obtain the results using equation (17):

( d H ) g ( t , u ) X ( g ( t , u ) ) Y ( f ( t , u ) ) = 0 ,

that is, ( d H ) g ( t , u ) X ( g ( t , u ) ) = Y ( H ( g ( t , u ) ) ) . As it is not difficult to show H ϕ t = ψ t H , it follows the second condition.□

Theorem 9 provides an equivalence of linear control systems and it is not difficult to show that this equivalence preserves the reachable sets from the identity. We denote these sets by

( X ) t = { g ( t , u ) : u L [ 0 , t ] and g ( 0 , u ) = e } ,

for t > 0 . Then we have the following proposition.

Proposition 10

Suppose that there exists a homomorphism H : G G such that (A) and (B) hold. Then H ( ( X ) t ) = ( Y ) t .

Proof

Let g ( t , u ) ( X ) t . From Theorem 9, we observe that H ( g ( t , u ) ) = H ( t , u ) , where H ( t , u ) ( Y ) t . Thus, h ( ( X ) t ) = ( Y ) t .□

We finish this section with the following remark.

Remark 11

With these results, it make sense to establish the following equivalence relation. Two systems are equivalent if there exists a group isomorphism H : G G such that the corresponding Lie algebra isomorphism ( d H ) e satisfies ( d H ) e ( D X ) = D Y ( d H ) e and ( d H ) e X i ( e ) = Y i ( H ( e ) ) , for every i = 1 , , n .

4 Conclusion

The main result, Theorem 1, provides a computable description of the solution of the linear system. This description is being applied to investigate the properties of this class of control systems. Recall that a classical topic of control theory is controllability. In our setup, it signifies the ability to navigate a system through its entire state space G using only permissible controls u . That is, consider a linear system on G as presented in the introduction, denote by g(t, u, h) its solution in h, then this system is called controllable if for all h 1 , h 2 G , there exist T > 0 and admissible control u such that g ( t , u , h 1 ) = h 2 for t ( o , T ) . Then it is clear the importance of a good description of the solution to study controllability. Another important concepts in control theory are the observability concept, which is a dual concept of controllability and stability. All these concepts needs of the solution of the system to be study [9]. We therefore hope that we will soon be able to apply the results of this article to study controllability. Finally, recall that the Jouan equivalence theorem allows us to extend any result of a linear control system on Lie groups to more general affine systems on manifolds which dynamics satisfy a finiteness condition, see reference [8].

Acknowledgements

The authors are grateful for the reviewer’s valuable comments, which helped to improve the manuscript.

  1. Funding information: A. J. Santana was partially supported by CNPq grant no. 309409/2023-3.

  2. Author contributions: VA: conceptualization, formal analysis, funding acquisition, reviewing and editing. AJS: supervision, investigation, funding acquisition and project administration. SNS: validation, formal analysis, methodology and visualization. MAV: software, resources, data curation and administration writing – original draft preparation. All authors have accepted responsibility for the entire content of this manuscript and consented to its submission to the journal, reviewed all the results, and approved the final version of the manuscript.

  3. Conflict of interest: The authors state no conflicts of interest.

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Received: 2024-08-10
Revised: 2024-10-25
Accepted: 2024-11-08
Published Online: 2024-12-31

© 2024 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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  61. Singularities of spherical surface in R4
  62. Variational approach to Kirchhoff-type second-order impulsive differential systems
  63. Convergence rate of the truncated Euler-Maruyama method for highly nonlinear neutral stochastic differential equations with time-dependent delay
  64. On the energy decay of a coupled nonlinear suspension bridge problem with nonlinear feedback
  65. The limit theorems on extreme order statistics and partial sums of i.i.d. random variables
  66. Hardy-type inequalities for a class of iterated operators and their application to Morrey-type spaces
  67. Solving multi-point problem for Volterra-Fredholm integro-differential equations using Dzhumabaev parameterization method
  68. Finite groups with gcd(χ(1), χc (1)) a prime
  69. Small values and functional laws of the iterated logarithm for operator fractional Brownian motion
  70. The hull-kernel topology on prime ideals in ordered semigroups
  71. ℐ-sn-metrizable spaces and the images of semi-metric spaces
  72. Strong laws for weighted sums of widely orthant dependent random variables and applications
  73. An extension of Schweitzer's inequality to Riemann-Liouville fractional integral
  74. Construction of a class of half-discrete Hilbert-type inequalities in the whole plane
  75. Analysis of two-grid method for second-order hyperbolic equation by expanded mixed finite element methods
  76. Note on stability estimation of stochastic difference equations
  77. Trigonometric integrals evaluated in terms of Riemann zeta and Dirichlet beta functions
  78. Purity and hybridness of two tensors on a real hypersurface in complex projective space
  79. Classification of positive solutions for a weighted integral system on the half-space
  80. A quasi-reversibility method for solving nonhomogeneous sideways heat equation
  81. Higher-order nonlocal multipoint q-integral boundary value problems for fractional q-difference equations with dual hybrid terms
  82. Noetherian rings of composite generalized power series
  83. On generalized shifts of the Mellin transform of the Riemann zeta-function
  84. Further results on enumeration of perfect matchings of Cartesian product graphs
  85. A new extended Mulholland's inequality involving one partial sum
  86. Power vector inequalities for operator pairs in Hilbert spaces and their applications
  87. On the common zeros of quasi-modular forms for Γ+0(N) of level N = 1, 2, 3
  88. One special kind of Kloosterman sum and its fourth-power mean
  89. The stability of high ring homomorphisms and derivations on fuzzy Banach algebras
  90. Integral mean estimates of Turán-type inequalities for the polar derivative of a polynomial with restricted zeros
  91. Commutators of multilinear fractional maximal operators with Lipschitz functions on Morrey spaces
  92. Vector optimization problems with weakened convex and weakened affine constraints in linear topological spaces
  93. The curvature entropy inequalities of convex bodies
  94. Brouwer's conjecture for the sum of the k largest Laplacian eigenvalues of some graphs
  95. High-order finite-difference ghost-point methods for elliptic problems in domains with curved boundaries
  96. Riemannian invariants for warped product submanifolds in Q ε m × R and their applications
  97. Generalized quadratic Gauss sums and their 2mth power mean
  98. Euler-α equations in a three-dimensional bounded domain with Dirichlet boundary conditions
  99. Enochs conjecture for cotorsion pairs over recollements of exact categories
  100. Zeros distribution and interlacing property for certain polynomial sequences
  101. Random attractors of Kirchhoff-type reaction–diffusion equations without uniqueness driven by nonlinear colored noise
  102. Study on solutions of the systems of complex product-type PDEs with more general forms in ℂ2
  103. Dynamics in a predator-prey model with predation-driven Allee effect and memory effect
  104. A note on orthogonal decomposition of 𝔰𝔩n over commutative rings
  105. On the δ-chromatic numbers of the Cartesian products of graphs
  106. Binomial convolution sum of divisor functions associated with Dirichlet character modulo 8
  107. Commutator of fractional integral with Lipschitz functions related to Schrödinger operator on local generalized mixed Morrey spaces
  108. System of degenerate parabolic p-Laplacian
  109. Stochastic stability and instability of rumor model
  110. Certain properties and characterizations of a novel family of bivariate 2D-q Hermite polynomials
  111. Stability of an additive-quadratic functional equation in modular spaces
  112. Monotonicity, convexity, and Maclaurin series expansion of Qi's normalized remainder of Maclaurin series expansion with relation to cosine
  113. On k-prime graphs
  114. On the existence of tripartite graphs and n-partite graphs
  115. Classifying pentavalent symmetric graphs of order 12pq
  116. Almost periodic functions on time scales and their properties
  117. Some results on uniqueness and higher order difference equations
  118. Coding of hypersurfaces in Euclidean spaces by a constant vector
  119. Cycle integrals and rational period functions for Γ0+(2) and Γ0+(3)
  120. Degrees of (L, M)-fuzzy bornologies
  121. A matrix approach to determine optimal predictors in a constrained linear mixed model
  122. On ideals of affine semigroups and affine semigroups with maximal embedding dimension
  123. Solutions of linear control systems on Lie groups
  124. A uniqueness result for the fractional Schrödinger-Poisson system with strong singularity
  125. On prime spaces of neutrosophic extended triplet groups
  126. On a generalized Krasnoselskii fixed point theorem
  127. On the relation between one-sided duoness and commutators
  128. Non-homogeneous BVPs for second-order symmetric Hamiltonian systems
  129. Erratum
  130. Erratum to “Infinitesimals via Cauchy sequences: Refining the classical equivalence”
  131. Corrigendum
  132. Corrigendum to “Matrix stretching”
  133. Corrigendum to “A comprehensive review of the recent numerical methods for solving FPDEs”
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