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Multiple and sign-changing solutions for discrete Robin boundary value problem with parameter dependence

  • Yuhua Long EMAIL logo and Baoling Zeng
Published/Copyright: December 29, 2017

Abstract

In this paper, we study second-order nonlinear discrete Robin boundary value problem with parameter dependence. Applying invariant sets of descending flow and variational methods, we establish some new sufficient conditions on the existence of sign-changing solutions, positive solutions and negative solutions of the system when the parameter belongs to appropriate intervals. In addition, an example is given to illustrate our results.

MSC 2010: 39A11

1 Introduction

Throughout this paper, let N, Z and R denote the sets of all nature numbers, integers and real numbers, respectively. We consider the following second-order nonlinear difference equation with Robin boundary value problem (BVP for short)

Δ2x(k1)=αf(k,x(k)),k[1,T],x(0)=Δx(T)=0, (1)

where T ≥ 2 is a given integer, [1,T] = :{1, 2, ⋯, T}, parameter α > 0, f:[1,TRR is continuous in the second variable, Δ denotes the forward difference operator defined by Δ x(k) = x(k+1)−x(k), Δ2 x(k) = Δ(Δ x(k)).

Discrete nonlinear equations with parameter dependence play an important role in describing many physical problems, such as nonlinear elasticity theory or mechanics and engineering topics [1, 2]. In recent years, some authors also contributed to the study of (1) and obtained some interesting results. For example, when α = 1, Jiang and Zhou [3] employed strongly monotone operator and critical point theory to establish the existence of nontrivial positive solutions. By virtue of variational methods and critical point theory, Guo and Song [4] investigated the existence of positive solutions. Zhang and Xu [5] obtained the existence and uniqueness theorems of nontrivial solutions. For results on nonlinear difference equations with other boundary value problems, we can see [6, 7] and references therein. With reference to the sign-changing solution, many scholars studied it for differential equations by a variety of methods and techniques, such as Leray-Schauder degree theory [8], fixed point index theory [9], topological degree theory [10], critical point theory and invariant sets of descending flow [11, 12, 13] etc. However, to the author’s knowledge, there were few papers [14] that considered the sign-changing solutions for discrete boundary problems. One of the reasons is the fact that the traditional pasting techniques of differential equations are not applicable in the world of difference equations. The corresponding anchoring techniques are rather complicated, see the detailed discussion in [15].

View from above reasons and motivated by [14], the purpose of this paper is to apply invariant sets of descending flow and variational techniques to get some sufficient conditions for the existence of sign-changing solutions, negative solutions and positive solutions to (1).

In the following, we first consider the linear eigenvalue problem corresponding to (1)

Δ2x(k1)=λx(k),k[1,T],x(0)=Δx(T)=0, (2)

Let λk be eigenvalues of (2) and {zk}k=1T be the corresponding eigenvectors of {λk}k=1T, then

λk=4sin2(2k12T+1π2),zk(j)=sin(2k1)πj2T+1,k,j=1,2,,T.

Obviously, λ1=4sin2π2(2T+1)>0 and z1(j)=sinjπ2T+1>0 for j ∈ [1,T].

In this paper, we focus on the following assumptions:

  1. f0=maxk[1,T]lim supu0|f(k,u)u|<λ1.

  2. lim|u|f(k,u)u=r for k ∈ [1,T], where r ∈ (0,+ ∞) is a constant, or r = + ∞, ν > 2 and C > 0 satisfy |f(k,u)| ≤ C(1+|u|ν−1),k ∈ [1,T], uR.

  3. Either (i) lim|u|[uf(k,u)2F(k,u)]=, uniformly for k ∈ [1,T],

    or (ii) lim|u|[uf(k,u)2F(k,u)]=+, uniformly for k ∈ [1,T],

where F(k,u)=0uf(k,s)ds.

Our results read as follows:

Theorem 1.1

Suppose (J1), (J2) hold and r > λ2α . If α12,+ and r is not an eigenvalue of (2), then (1) has at least three nontrivial solutions, one sign-changing, one positive and one negative.

Theorem 1.2

Suppose (J1)–(J3) hold and r > λ2α . If r is an eigenvalue of (2), then (1) has at least three nontrivial solutions, one sign-changing, one positive and one negative.

The remainder of this paper is organized as follows. After introducing some notations and preliminary results in Section 2, we complete the proof of Theorem 1.1 and give an example to illustrate our result in Section 3.

2 Variational structure and preliminary results

Given m ≥ 0, let G = {x:[0,T+1]→ R|x(0) = Δ x(T) = 0} be a T-dimensional Hilbert space which is equipped with the inner product

x,ym=k=1T[Δx(k1)Δy(k1)+mx(k)y(k)],forallx,yG,

then the induced norm ∥⋅∥m is

xm=(k=1T[|Δx(k1)|2+m|x(k)|2])12,forallxG.

Let H be the T-dimensional Hilbert space equipped with the usual inner product (⋅,⋅) and norm ∥⋅∥. It is easy to see that G is isomorphic to H, ∥⋅∥m and ∥⋅∥ are equivalent. Denote x+ = max{x,0},x = min{x,0}. Then for any xH, 〈 ⋅,⋅〉 m ≥ 0.

Define functional I:H→ as

I(x)=12k=1T|Δx(k1)|2αk=1TF(k,x(k)). (3)

For any x = (x(1), x(2), ⋯, x(T))H, I(x) can be rewritten as

I(x)=12(Ax,x)αk=1TF(k,x(k)), (4)

here ατ is the transpose of the vector α on H, A is T× T matrix

2100012100012000002100011.

Remark 2.1

In fact, many existing results are applicable. Namely, one can apply numerous results for the variational formulation (4), see [16, 17, 18].

For m ≥ 0, consider BVP

Δ2x(k1)+mx(k)=h(k),k[1,T],x(0)=Δx(T)=0, (5)

where h:[1,T]→R. It is not hard to see that (5) and the system of linear algebra equations (A+mI)x = h are equivalent, then the unique solution of (5) can be expressed by

x=(A+mI)1h. (6)

On the other side, we have

Lemma 2.2

The unique solution of (5) is

x(k)=s=1TGm(k,s)h(s),k[0,T+1],

here Gm(k,s) can be written as

Gm(k,s)=(pTspsTpT+1s+psT1)(pkpk)W,0ksT+1,(pTkpkTpT+1k+pkT1)(psps)W,0skT+1,

W = (pT+1−pT−1pT+pT)(p−1p), p=2+m+4m+m22.

Proof

First study the homogeneous equation of (5)

Δ2x(k1)+mx(k)=0,k[1,T],x(0)=Δx(T)=0, (7)

then the corresponding characteristic equation of (7) is p2−(2+m)p+1 = 0. Consider m > 0 (m = 0 is trivial), then (2+m)2−4 > 0, which means we have

p1=2+m+4m+m22,p2=2+m4m+m22.

Then two independent solutions of (7) can be expressed by x1(k) = p1k and x2(k) = p2k . Therefore, the general solution of (5) is x(k) = a1(k) p1k +a2(k) p2k .

The next step is to determine coefficients a1(k) and a2(k). Using the method of variation of constant, we get the general solution of (5) as

x(k)=a1(0)+s=1kp2sh(s)p2p1p1k+a2(0)s=1kp1sh(s)p2p1p2k.

From initial conditions, we find a1(0) = −a2(0) and

a1(0)=s=1T(p1Tp2sp1sp2Tp2sp1T+1+p1sp2T+1)(p1T+1p2T+1p1T+p2T)(p2p1)h(s).

Write W=(p1T+1p2T+1p1T+p2T)(p2p1),p1=p21=p, then

x(k)=1W[s=1T(pTspsTpT+1s+psT1)(pkpk)+s=1k(PksPsk)(pT+1pT1pT+pT)]h(s)

which means the proof of Lemma 2.2 is completed. □

Remark 2.3

From Lemma 2.2, for k,s ∈ [1,T], there holds Gm(k,s) = Gm(s,k) > 0. For any xH, k ∈ [1,T], define Km, fm, Am:HH as follows

(Kmx)(k)=s=1TGm(k,s)x(s),(fmx)(k)=f(k,x(k))+mx(k),Am=Kmfm

where Am:HH is a completely continuous operator. Combining (6) with Lemma 2.2, we get Km = (A+mI)−1.

Remark 2.4

According to Lemma 2.2, it is not difficult to see that {x(k)}k=0T+1 is a solution of (1) if and only if x={x(k)}k=1TH is a fixed point of Am.

Lemma 2.5

The functional I defined by (3) is Fréchet differentiable on H and I′(x) has the expression I′(x) = xKm fmx for xH.

Proof

For any x,yH, using the mean value theorem, it follows I(x+y)I(x)=12k=1T|Δy(k1)|2+k=1T[Δx(k1)Δy(k1)αf(k,x(k)+θ(k)y(k))y(k)],

here θ(k) ∈ (0,1), k ∈ [1,T]. As f is continuous in x, we find

I(x+y)I(x)x,ym+k=1T(αf(k,x(k))+mx(k))y(k)=ymo(1)

which leads to

limym01ym(αk=1T[f(k,y(k)f(k,x(k)+θ(k)y(k)))y(k)]+12ym212my2)=0,

thus I is Fréchet differentiable on H and

I(x),ym=x,ymk=1T(αf(k,x(k))+mx(k))y(k). (8)

On the other side, for all x = {x(k)} ∈ H, z = {z(k)} ∈ H, there holds

k=1TΔ2x(k1)y(k)=k=1T[Δx(k)y(k)Δx(k1)y(k)]=k=1TΔx(k1)Δy(k1).

Making use of the definition of inner product and Lemma 2.2, we get

xKmfmx,ym=x,ymk=1T(αf(k,x(k))+mx(k))y(k)

then 〈I′(x),ym = 〈xKmfmx,ym for all x,yH, i.e., IȲ(x) = xKm fmx. This completes the proof of Lemma 2.5. □

Remark 2.6

According to Lemma 2.5 and Remark 2.4, we find out that critical points of I defined on H are precisely solutions of (1).

Definition 2.7

([19]). Let I be a C1 functional defined on E. I is said to satisfy Palais-Smale condition ((PS)condition for short) if any sequence {un} ⊂ E for which I(un) is bounded and I′(un) → 0(n → ∞) possesses a convergent subsequence in E.

Definition 2.8

([20]). Assume I be a C1 functional defined on E. If any sequence {un} such that I(un) is bounded and (1+∥unm)∥I′(un)∥m → 0 as n → ∞ has a convergent subsequence in E, then we say that I satisfies the Cerami condition ((C) condition for short).

Lemma 2.9

([21]). Let H be a Hilbert space, there are two open convex subsets B1 and B2 on H with Am( B1) ⊂ B1, Am( B2) ⊂ B2 and B1B2 ≠ ∅. If IC1(H,R) satisfies the (PS) condition and I′(x) = xAmx for all xH. Assume there is a path g:[0,1] → H such that

g(0)B1B2,g(1)B2B1,

and

infuB1¯B2¯I(x)>supτ[0,1]I(g(τ)),

then I has at least four critical points, one in H ∖(B1B2), one in B1B2, one in B1B2, and one in B2B1.

Remark 2.10

By Theorem 5.1 [20], we can replace (PS) condition by weaker (C) condition in Lemma 2.9.

In this paper, we will analyse the properties of the flow, pay close attention to the direction and the destination to which the flow goes, and seek the limit along the flow. We are interested in those points in H across which the flow does not go to infinity and work for seeking such points in H. If we have such a point, then the flow curve crossing it goes ultimately to a critical point. It seems that one would obtain many critical points if he or she is given many such points. However, even if there may be many such points, we cannot get more than one critical point in general since the different flow curves may ultimately go to the same critical point. In order to get more critical points, we will define the concept of invariant set of descending flow and then we will divide the whole space H into several invariant subsets of descending flow. In this way, we can get more than one critical point.

3 Proof of main result

Let convex cones Λ = {xH:x ≥ 0} and −Λ = {xH:x ≤ 0}. The distance respecting to ∥⋅∥m in H is written by distm. For arbitrary ε > 0, we denote

Bε+={xH:distm(x,Λ)<ε},Bε={xH:distm(x,Λ)<ε}.

Notice that Bε+ and Bε are open convex subsets on H with Bε+Bε and H(Bε+Bε) contains only sign-changing functions.

Lemma 3.1

Suppose one of the following condition holds.

  1. r = + ∞ or

  2. r < + ∞ is not an eigenvalue of (2), here r is defined by (J2).

Then the functional I defined by (3) satisfies (PS) condition for all α12,+.

Proof

  1. Assume r = + ∞. Let {xn} ⊂ H be a (PS) sequence. Since H is a finite dimensional space, we only need to show {xn} is bounded. If r = + ∞, choosing a constant y > 0, for all (k,u) ∈ [1,TR, we have F(k,u) ≥ λT u2y. Then

    I(xn)=12(Axn,xn)αk=1TF(k,xn(k))12αλTxn2+Tαy, (9)

    thus xn22I(xn)2Tαy(12α)λT is bounded for α>12.

  2. suppose r < + ∞ is not an eigenvalue of (2). We are now ready to prove that {xn} is bounded. Arguing by contradiction, we suppose there is a subsequence of {xn} with ρn = ∥xn∥ → + ∞ as n → ∞ and for each k ∈ [1,T], either {xn(k)} is bounded or xn(k) → + ∞. Put yn=xnρn. Clearly, ∥yn∥ = 1. Then there have a subsequence of {yn} and yH satisfying that yny as n → ∞. Write dn = f(1,xn(1))xn(1)yn(1),...,f(T,xn(T))xn(T)yn(T).

    Since lim|u|+f(k,u)u=r for all k ∈ [1,T] and I′(xn) = xnKm fmxn, we get

    I(xn)ρn=yn1ρnK0f0xn=ynK0dnyK0ry.

    For I(xn)ρn0 as n → ∞, we have yK0ry → 0. In view of Lemma 2.5, we find that r is an eigenvalue of matrix A, which contradicts the assumption. So {xn} is bounded and the proof is finished. □

Lemma 3.2

I satisfies (C) condition under (J3).

Proof

First assume (J3)(i) is satisfied. There exists a constant M1 > 0 such that {xn} ⊂ H with I(xn) ≤ M1 and (1+∥xnm)∥I′(xn)∥mM1, then

3M1αk=1T[xn(k)f(k,xn(k))2F(k,xn(k))]. (10)

We claim {xn} is bounded. Actually, if {xn} is unbounded, it possesses a subsequence of {xn} and some k0 ∈ [1,T] satisfying |xn(k0)| → + ∞ as n → ∞. According to (J3)(i), we get

xn(k0)f(k0,xn(k0))2F(k0,xn(k0))asn,

and there is a constant M2 > 0 such that uf(k,u)−2F(k,u) ≤ M2 for any k ∈ [1,T] and uR. Therefore,

k=1T[xn(k)f(k,xn(k))2F(k,xn(k))]

which contradicts (10). So our claim is proved and I satisfies the (C) condition.

Finally, assume (J3)(ii) hold. In a similar way as above, we find that I satisfies (C) condition. Then Lemma 3.2 is verified. □

Lemma 3.3

If (J1) and (J2) hold, there exist m ≥ 0 and ε0 > 0 such that for 0 < ε < ε0, we have:

  1. if xBε is a nontrivial critical point of I and Am(Bε)Bε, then x is a negative solution of (1);

  2. if xBε+ is a nontrivial critical point of I and Am(Bε+)Bε+, then x is a positive solution of (1).

Proof

  1. According to (J1) and (J2), for all u ≠ 0 and k ∈ [1,T], there exists m ≥ 0 such that

    u(αf(k,u)+mu)>0. (11)

    Let y = Am(x) and x+ = max{x,0}, x = min{x,0} for x ∈ H. Since

    xm2=k=1T[|Δx(k1)|2+m|x(k)|2]=xτAx+mx2=λx2+mx2=(λ+m)x2,

    it follows λ1+mxxmλT+mx and

    x+=infzΛxz1m+λ1infzΛxzm=1m+λ1distm(x,Λ). (12)

    By (J1) and (J2), there exist constants τ > 0, C > 0 and ν > 2 such that

    |αf(k,u)+mu|(m+λ1τ)|u|+αC|u|ν1,(k,u)[1,T]×R. (13)

    Choosing a constant D > 0, since xH, we have

    |x|ν:=(k=1T|x(k)|ν)1νDmin{x,xm},xH. (14)

    It is obvious that |x|2 = ∥x∥. Moreover, y+ = yy and y ∈ −Λ imply distm(y,−Λ) ≤ ∥yym = ∥y+m. Making use of (12), (15) and (14), we get

    distm(y,Λ)y+m(m+λ1τm+λ1distm(x,Λ)+C1(distm(x,Λ))ν1)y+m,

    here C1=αCDν(m+λ1)ν1. Hence

    distm(y,Λ)m+λ1τm+λ1distm(x,Λ)+C1(distm(x,Λ))ν1.

    Let C1(distm(x,Λ))ν2=τ2(m+λ1), there holds

    distm(Am(x),Λ)2(m+λ1)τ2(m+λ1)distm(x,Λ). (15)

    Since 2(m+λ1)τ2(m+λ1)<1, we obtain

    Am(x)Bε,uBε.

    If xBε is a nontrivial critical point of I, it is clear that I′(x) = xAmx = 0. It follows from (15) that x ∈ −Λ ∖{0}. Combining (11) and remark 2.3, we have x(k) < 0. Consequently, x is a negative solution of (1).

  2. can be discussed similarly, we only need to change y+ to y to prove (ii). For simplicity, we omit its proof. □

Lemma 3.4

Suppose z1,z2 be eigenvectors corresponding to eigenvalues λ1,λ2 of (2) and uH2 = span{z1,z2}. If r>λ2α, then I(x) → − ∞ asxm → + ∞.

Proof

  1. If r = + ∞. From (9), for any xH, we have I(x) → −∞ as ∥xm → + ∞.

  2. Assume rλ2α,+. For uH2, x = ε1 z1+ε2 z2. In general, we can suppose (z1,z2) = 0. Thus x2=x,x=ε1z1+ε2z2,ε1z1+ε2z2=ε12z12+ε22z22 and there exists ε satisfying 0 < ε < minrλ1α,rλ2α. From lim|x|+f(k,x)x=r, for any k ∈ [1,T] and xR, there exists a constant ζ > 0 such that F(k,x)rε2x2ζ.

    Then for xH2, it follows

    I(x)12(λ1αr+αε)ε12z12+12(λ2αr+αε)ε22z22+Tζα.

    That is, I(x) → −∞ as ∥xm → + ∞ for λ1α r+α ε < 0 and λ2α r+α ε < 0. □

Now we are in the position to prove Theorem 1.1 by using Lemma 2.9.

Proof of Theorem 1.1

From (15), we get αF(k,x)+m2|x|2(m+λ1τ)12|x|2+αCν|x|ν, which together with (14) gives that

I(x)τ2(m+λ1)xm2αCDννxmν.

It follows from (12) that x±1m+λ1distm(x,Λ)1m+λ1ε0 for any xBε+¯Bε¯. Then there is c0 > −∞ such that infxBε+¯Bε¯I(x)=c0. Moreover, in view of Lemma 3.4, we can choose R > 2ε0 such that I(x) < c0−1 for all xH2 and ∥xm = R. To apply Lemma 2.9, we define a path g:[0,1] → H2 as

g(s)=Rz1cos(πs)+z2sin(πs)z1cos(πs)+z2sin(πs)m.

By direct computation, we get

g(0)=Rz1z1mBε+Bε,g(1)=Rz1z1mBεBε+,infxBε+¯Bε¯I(x)>supτ[0,1]I(g(τ)).

Combining Lemmas 3.1, 3.3 and 2.9, we find there is a critical point in H(Bε+¯Bε¯) corresponding to a sign-changing solution of (1). Moreover, we also have a critical point in Bε+Bε¯(BεBε+¯) corresponding to a positive solution(a negative solution) of (1). The proof is completed. □

Remark 3.5

By Lemma 3.2 and Remark 2.10, we find the proof of Theorem 1.2 is analogous to the proof of Theorem 1.1 and we therefore omit it.

Finally, we exhibit an example to illustrate Theorem 1.1.

Example 3.6

Consider (1) with α = 2 and f(k,x)=|x|n|x|+1mx. Here m>2sin23π2(2T+1), 0 < n < 4sin2π2(2T+1)m. Then

F(k,u)=mx22m(n+1)(xln(1+x)),x0,mx22+m(n+1)(x+ln(1x)),x<0.

By direct computation, we have lim|x|[2F(k,x)xf(k,x)]= uniformly for k ∈ [1,T] and λ1 = 4sin2π2(2T+1),λ2=4sin23π2(2T+1). In addition, f0=maxk[1,T]lim supx0|f(k,x)x|=mn<λ1 and lim|x|f(k,x)x=r=m>λ22. Then (1) satisfies conditions of Theorem 1.1, thus it has at least a positive solution, a negative solution and a sign-changing solution.

For the case T = 2, here m>2sin23π101.28,0<n<4sin2π10m0.36m, thus we can choose m = 1.5 and n = 0.1. After not very complicated calculation, we find (0, 0.161, 0.298,0.298), (0,8.73,−5.77,−5.77), (0, −0.1616, −0.2975,−0.2975) and (0,−8.73,5.77,5.77) are nontrivial approximate solutions of (1).

Acknowledgement

This work is supported by the Program for Changjiang Scholars and Innovative Research Team in University (IRT16R16).

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Received: 2017-8-2
Accepted: 2017-10-24
Published Online: 2017-12-29

© 2017 Long and Zeng

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

Articles in the same Issue

  1. Regular Articles
  2. Integrals of Frullani type and the method of brackets
  3. Regular Articles
  4. Edge of chaos in reaction diffusion CNN model
  5. Regular Articles
  6. Calculus using proximities: a mathematical approach in which students can actually prove theorems
  7. Regular Articles
  8. An investigation on hyper S-posets over ordered semihypergroups
  9. Regular Articles
  10. The Leibniz algebras whose subalgebras are ideals
  11. Regular Articles
  12. Fixed point and multidimensional fixed point theorems with applications to nonlinear matrix equations in terms of weak altering distance functions
  13. Regular Articles
  14. Matrix rank and inertia formulas in the analysis of general linear models
  15. Regular Articles
  16. The hybrid power mean of quartic Gauss sums and Kloosterman sums
  17. Regular Articles
  18. Tauberian theorems for statistically (C,1,1) summable double sequences of fuzzy numbers
  19. Regular Articles
  20. Some properties of graded comultiplication modules
  21. Regular Articles
  22. The characterizations of upper approximation operators based on special coverings
  23. Regular Articles
  24. Bi-integrable and tri-integrable couplings of a soliton hierarchy associated with SO(4)
  25. Regular Articles
  26. Dynamics for a discrete competition and cooperation model of two enterprises with multiple delays and feedback controls
  27. Regular Articles
  28. A new view of relationship between atomic posets and complete (algebraic) lattices
  29. Regular Articles
  30. A class of extensions of Restricted (s, t)-Wythoff’s game
  31. Regular Articles
  32. New bounds for the minimum eigenvalue of 𝓜-tensors
  33. Regular Articles
  34. Shintani and Shimura lifts of cusp forms on certain arithmetic groups and their applications
  35. Regular Articles
  36. Empirical likelihood for quantile regression models with response data missing at random
  37. Regular Articles
  38. Convex combination of analytic functions
  39. Regular Articles
  40. On the Yang-Baxter-like matrix equation for rank-two matrices
  41. Regular Articles
  42. Uniform topology on EQ-algebras
  43. Regular Articles
  44. Integrations on rings
  45. Regular Articles
  46. The quasilinear parabolic kirchhoff equation
  47. Regular Articles
  48. Avoiding rainbow 2-connected subgraphs
  49. Regular Articles
  50. On non-Hopfian groups of fractions
  51. Regular Articles
  52. Singularly perturbed hyperbolic problems on metric graphs: asymptotics of solutions
  53. Regular Articles
  54. Rings in which elements are the sum of a nilpotent and a root of a fixed polynomial that commute
  55. Regular Articles
  56. Superstability of functional equations related to spherical functions
  57. Regular Articles
  58. Evaluation of the convolution sum involving the sum of divisors function for 22, 44 and 52
  59. Regular Articles
  60. Weighted minimal translation surfaces in the Galilean space with density
  61. Regular Articles
  62. Complete convergence for weighted sums of pairwise independent random variables
  63. Regular Articles
  64. Binomials transformation formulae for scaled Fibonacci numbers
  65. Regular Articles
  66. Growth functions for some uniformly amenable groups
  67. Regular Articles
  68. Hopf bifurcations in a three-species food chain system with multiple delays
  69. Regular Articles
  70. Oscillation and nonoscillation of half-linear Euler type differential equations with different periodic coefficients
  71. Regular Articles
  72. Osculating curves in 4-dimensional semi-Euclidean space with index 2
  73. Regular Articles
  74. Some new facts about group 𝒢 generated by the family of convergent permutations
  75. Regular Articles
  76. lnfinitely many solutions for fractional Schrödinger equations with perturbation via variational methods
  77. Regular Articles
  78. Supersolvable orders and inductively free arrangements
  79. Regular Articles
  80. Asymptotically almost automorphic solutions of differential equations with piecewise constant argument
  81. Regular Articles
  82. Finite groups whose all second maximal subgroups are cyclic
  83. Regular Articles
  84. Semilinear systems with a multi-valued nonlinear term
  85. Regular Articles
  86. Positive solutions for Hadamard differential systems with fractional integral conditions on an unbounded domain
  87. Regular Articles
  88. Calibration and simulation of Heston model
  89. Regular Articles
  90. One kind sixth power mean of the three-term exponential sums
  91. Regular Articles
  92. Cyclic pairs and common best proximity points in uniformly convex Banach spaces
  93. Regular Articles
  94. The uniqueness of meromorphic functions in k-punctured complex plane
  95. Regular Articles
  96. Normalizers of intermediate congruence subgroups of the Hecke subgroups
  97. Regular Articles
  98. The hyperbolicity constant of infinite circulant graphs
  99. Regular Articles
  100. Scott convergence and fuzzy Scott topology on L-posets
  101. Regular Articles
  102. One sided strong laws for random variables with infinite mean
  103. Regular Articles
  104. The join of split graphs whose completely regular endomorphisms form a monoid
  105. Regular Articles
  106. A new branch and bound algorithm for minimax ratios problems
  107. Regular Articles
  108. Upper bound estimate of incomplete Cochrane sum
  109. Regular Articles
  110. Value distributions of solutions to complex linear differential equations in angular domains
  111. Regular Articles
  112. The nonlinear diffusion equation of the ideal barotropic gas through a porous medium
  113. Regular Articles
  114. The Sheffer stroke operation reducts of basic algebras
  115. Regular Articles
  116. Extensions and improvements of Sherman’s and related inequalities for n-convex functions
  117. Regular Articles
  118. Classification lattices are geometric for complete atomistic lattices
  119. Regular Articles
  120. Possible numbers of x’s in an {x, y}-matrix with a given rank
  121. Regular Articles
  122. New error bounds for linear complementarity problems of weakly chained diagonally dominant B-matrices
  123. Regular Articles
  124. Boundedness of vector-valued B-singular integral operators in Lebesgue spaces
  125. Regular Articles
  126. On the Golomb’s conjecture and Lehmer’s numbers
  127. Regular Articles
  128. Some applications of the Archimedean copulas in the proof of the almost sure central limit theorem for ordinary maxima
  129. Regular Articles
  130. Dual-stage adaptive finite-time modified function projective multi-lag combined synchronization for multiple uncertain chaotic systems
  131. Regular Articles
  132. Corrigendum to: Dual-stage adaptive finite-time modified function projective multi-lag combined synchronization for multiple uncertain chaotic systems
  133. Regular Articles
  134. Convergence and stability of generalized φ-weak contraction mapping in CAT(0) spaces
  135. Regular Articles
  136. Triple solutions for a Dirichlet boundary value problem involving a perturbed discrete p(k)-Laplacian operator
  137. Regular Articles
  138. OD-characterization of alternating groups Ap+d
  139. Regular Articles
  140. On Jordan mappings of inverse semirings
  141. Regular Articles
  142. On generalized Ehresmann semigroups
  143. Regular Articles
  144. On topological properties of spaces obtained by the double band matrix
  145. Regular Articles
  146. Representing derivatives of Chebyshev polynomials by Chebyshev polynomials and related questions
  147. Regular Articles
  148. Chain conditions on composite Hurwitz series rings
  149. Regular Articles
  150. Coloring subgraphs with restricted amounts of hues
  151. Regular Articles
  152. An extension of the method of brackets. Part 1
  153. Regular Articles
  154. Branch-delete-bound algorithm for globally solving quadratically constrained quadratic programs
  155. Regular Articles
  156. Strong edge geodetic problem in networks
  157. Regular Articles
  158. Ricci solitons on almost Kenmotsu 3-manifolds
  159. Regular Articles
  160. Uniqueness of meromorphic functions sharing two finite sets
  161. Regular Articles
  162. On the fourth-order linear recurrence formula related to classical Gauss sums
  163. Regular Articles
  164. Dynamical behavior for a stochastic two-species competitive model
  165. Regular Articles
  166. Two new eigenvalue localization sets for tensors and theirs applications
  167. Regular Articles
  168. κ-strong sequences and the existence of generalized independent families
  169. Regular Articles
  170. Commutators of Littlewood-Paley gκ -functions on non-homogeneous metric measure spaces
  171. Regular Articles
  172. On decompositions of estimators under a general linear model with partial parameter restrictions
  173. Regular Articles
  174. Groups and monoids of Pythagorean triples connected to conics
  175. Regular Articles
  176. Hom-Lie superalgebra structures on exceptional simple Lie superalgebras of vector fields
  177. Regular Articles
  178. Numerical methods for the multiplicative partial differential equations
  179. Regular Articles
  180. Solvable Leibniz algebras with NFn Fm1 nilradical
  181. Regular Articles
  182. Evaluation of the convolution sums ∑al+bm=n lσ(l) σ(m) with ab ≤ 9
  183. Regular Articles
  184. A study on soft rough semigroups and corresponding decision making applications
  185. Regular Articles
  186. Some new inequalities of Hermite-Hadamard type for s-convex functions with applications
  187. Regular Articles
  188. Deficiency of forests
  189. Regular Articles
  190. Perfect codes in power graphs of finite groups
  191. Regular Articles
  192. A new compact finite difference quasilinearization method for nonlinear evolution partial differential equations
  193. Regular Articles
  194. Does any convex quadrilateral have circumscribed ellipses?
  195. Regular Articles
  196. The dynamic of a Lie group endomorphism
  197. Regular Articles
  198. On pairs of equations in unlike powers of primes and powers of 2
  199. Regular Articles
  200. Differential subordination and convexity criteria of integral operators
  201. Regular Articles
  202. Quantitative relations between short intervals and exceptional sets of cubic Waring-Goldbach problem
  203. Regular Articles
  204. On θ-commutators and the corresponding non-commuting graphs
  205. Regular Articles
  206. Quasi-maximum likelihood estimator of Laplace (1, 1) for GARCH models
  207. Regular Articles
  208. Multiple and sign-changing solutions for discrete Robin boundary value problem with parameter dependence
  209. Regular Articles
  210. Fundamental relation on m-idempotent hyperrings
  211. Regular Articles
  212. A novel recursive method to reconstruct multivariate functions on the unit cube
  213. Regular Articles
  214. Nabla inequalities and permanence for a logistic integrodifferential equation on time scales
  215. Regular Articles
  216. Enumeration of spanning trees in the sequence of Dürer graphs
  217. Regular Articles
  218. Quotient of information matrices in comparison of linear experiments for quadratic estimation
  219. Regular Articles
  220. Fourier series of functions involving higher-order ordered Bell polynomials
  221. Regular Articles
  222. Simple modules over Auslander regular rings
  223. Regular Articles
  224. Weighted multilinear p-adic Hardy operators and commutators
  225. Regular Articles
  226. Guaranteed cost finite-time control of positive switched nonlinear systems with D-perturbation
  227. Regular Articles
  228. A modified quasi-boundary value method for an abstract ill-posed biparabolic problem
  229. Regular Articles
  230. Extended Riemann-Liouville type fractional derivative operator with applications
  231. Topical Issue on Topological and Algebraic Genericity in Infinite Dimensional Spaces
  232. The algebraic size of the family of injective operators
  233. Topical Issue on Topological and Algebraic Genericity in Infinite Dimensional Spaces
  234. The history of a general criterium on spaceability
  235. Topical Issue on Topological and Algebraic Genericity in Infinite Dimensional Spaces
  236. On sequences not enjoying Schur’s property
  237. Topical Issue on Topological and Algebraic Genericity in Infinite Dimensional Spaces
  238. A hierarchy in the family of real surjective functions
  239. Topical Issue on Topological and Algebraic Genericity in Infinite Dimensional Spaces
  240. Dynamics of multivalued linear operators
  241. Topical Issue on Topological and Algebraic Genericity in Infinite Dimensional Spaces
  242. Linear dynamics of semigroups generated by differential operators
  243. Special Issue on Recent Developments in Differential Equations
  244. Isomorphism theorems for some parabolic initial-boundary value problems in Hörmander spaces
  245. Special Issue on Recent Developments in Differential Equations
  246. Determination of a diffusion coefficient in a quasilinear parabolic equation
  247. Special Issue on Recent Developments in Differential Equations
  248. Homogeneous two-point problem for PDE of the second order in time variable and infinite order in spatial variables
  249. Special Issue on Recent Developments in Differential Equations
  250. A nonlinear plate control without linearization
  251. Special Issue on Recent Developments in Differential Equations
  252. Reduction of a Schwartz-type boundary value problem for biharmonic monogenic functions to Fredholm integral equations
  253. Special Issue on Recent Developments in Differential Equations
  254. Inverse problem for a physiologically structured population model with variable-effort harvesting
  255. Special Issue on Recent Developments in Differential Equations
  256. Existence of solutions for delay evolution equations with nonlocal conditions
  257. Special Issue on Recent Developments in Differential Equations
  258. Comments on behaviour of solutions of elliptic quasi-linear problems in a neighbourhood of boundary singularities
  259. Special Issue on Recent Developments in Differential Equations
  260. Coupled fixed point theorems in complete metric spaces endowed with a directed graph and application
  261. Special Issue on Recent Developments in Differential Equations
  262. Existence of entropy solutions for nonlinear elliptic degenerate anisotropic equations
  263. Special Issue on Recent Developments in Differential Equations
  264. Integro-differential systems with variable exponents of nonlinearity
  265. Special Issue on Recent Developments in Differential Equations
  266. Elliptic operators on refined Sobolev scales on vector bundles
  267. Special Issue on Recent Developments in Differential Equations
  268. Multiplicity solutions of a class fractional Schrödinger equations
  269. Special Issue on Recent Developments in Differential Equations
  270. Determining of right-hand side of higher order ultraparabolic equation
  271. Special Issue on Recent Developments in Differential Equations
  272. Asymptotic approximation for the solution to a semi-linear elliptic problem in a thin aneurysm-type domain
  273. Topical Issue on Metaheuristics - Methods and Applications
  274. Learnheuristics: hybridizing metaheuristics with machine learning for optimization with dynamic inputs
  275. Topical Issue on Metaheuristics - Methods and Applications
  276. Nature–inspired metaheuristic algorithms to find near–OGR sequences for WDM channel allocation and their performance comparison
  277. Topical Issue on Cyber-security Mathematics
  278. Monomial codes seen as invariant subspaces
  279. Topical Issue on Cyber-security Mathematics
  280. Expert knowledge and data analysis for detecting advanced persistent threats
  281. Topical Issue on Cyber-security Mathematics
  282. Feedback equivalence of convolutional codes over finite rings
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