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A new approach to Jacobsthal, Jacobsthal-Lucas numbers and dual vectors

  • This paper gives a detailed study of a new generation of dual Jacobsthal and dual Jacobsthal-Lucas numbers using dual numbers. Also some formulas, facts and properties about these numbers are presented. In addition, a new dual vector called the dual Jacobsthal vector is presented. Some properties of this vector apply to various properties of geometry which are not generally known in the geometry of dual space. Finally, this study introduces the dual Jacobsthal and the dual Jacobsthal-Lucas numbers with coefficients of dual numbers. Some fundamental identities are demonstrated, such as the generating function, the Binet formulas, the Cassini's, Catalan's and d'Ocagne identities for these numbers.

    Citation: Faik Babadağ. A new approach to Jacobsthal, Jacobsthal-Lucas numbers and dual vectors[J]. AIMS Mathematics, 2023, 8(8): 18596-18606. doi: 10.3934/math.2023946

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  • This paper gives a detailed study of a new generation of dual Jacobsthal and dual Jacobsthal-Lucas numbers using dual numbers. Also some formulas, facts and properties about these numbers are presented. In addition, a new dual vector called the dual Jacobsthal vector is presented. Some properties of this vector apply to various properties of geometry which are not generally known in the geometry of dual space. Finally, this study introduces the dual Jacobsthal and the dual Jacobsthal-Lucas numbers with coefficients of dual numbers. Some fundamental identities are demonstrated, such as the generating function, the Binet formulas, the Cassini's, Catalan's and d'Ocagne identities for these numbers.



    In 1873, W. K. Clifford initiated the study of dual numbers and these numbers were used at the beginning of the twentieth century by the German mathematician Eduard Study, who studied line geometry and kinematics to obtain the dual angle which measures the relative position of two skew lines in space. This study defines a dual angle as  θ+dε, where θ is the angle between the directions of two lines in three-dimensional space and d is a distance between them, [1,2,3].

    In this paper, our objective is to conduct a detailed study of a new generation of the dual Jacobsthal number and dual Jacobsthal-Lucas numbers. We describe a new dual Jacobsthal vector to apply in the geometry of dual space.

    A dual number is described as U=u+εu, where u and u are real numbers and ε is a symbol taken to satisfy  ε2=0 with  ε0.

    The addition and multiplication of two dual numbers U=u+εu and V=v+εv are defined by

    U+V=(u+v)+ ε(u+v)

    and

    UV=uv+ε(uv+uv),

    respectively. In mathematics and physics, vector is a term that refers to some quantities that cannot be expressed by a single number (a scalar) or to elements of some vector spaces as in [4].

    The dual vector D3 is defined by

    U=u+εu ;u,uϵR3=(u1+εu1,u2+εu2,u3+εu3).

    The scalar product and cross product of dual vectors U=u+εu and V=v+ εv are

    U,V=u,v+ε(u,v+u,v), (1.1)

    and

    U×V=u,v+ε(u×v+u×v), (1.2)

    respectively.

    The norm of the dual vector U is given by

    U=u+u,uu.

    Proposition 1. U is dual unit vector if and only if u=1 and u,u=0 [1].

    The Jacobsthal numbers and the Jacobsthal-Lucas numbers are given by the second-order recurrence relations as follows:

    Jn=Jn1+2Jn2,J0=0,J1=1,

    and

    jn=jn1+2jn2,j0=2, j1=1,

    respectively, [5,6,7,8,9,10,11,12]. Also these numbers each have another expression of the respective forms

    Jn=αnβn    αβ=2n(1)n3, (1.3)

    and

    jn=αn+βn=2n+(1)n. (1.4)

    The dual Jacobsthal numbers and the dual Jacobsthal-Lucas numbers, respectively, are as follows:

    Jn=Jn+εJn+1, (1.5)

    and

    jn=jn+εjn+1, (1.6)

    where ε2=0 with  ε0.

    In this section, we obtain some fundamental identities such as the generating function, the Binet formulas, the Cassini's, Catalan's and d'Ocagne identities for the dual Jacobsthal numbers and the dual Jacobsthal-Lucas numbers.

    Theorem 1. The generating function of Jn is

    h(t)=J0(1t)+   J1t1t2t2.

    Proof. If h(t) is a generating function for Jn, then

    h(t)=i=0Jiti.

    Multiply the function h(t) by t and t2, respectively. We can write

    th(t)=J0t+J21t+...+Jn+1nt,t2h(t)=J0t2+J1t3+...+Jntn+2.

    Doing the needed arrangements, we will have

    h(t)(1t2t2)=J0+t(J1J0),h(t)=i=0Ji ti

    which is the desired result.

    Theorem 2. Let Jn and Jm be dual Jacobsthal numbers. For every m,n1,

    JnJm+Jn+1Jm+1=19(jn+m2m(1)mjnm)+ε19(2n+m+4+12Jn+m+2m(1)mjnm).

    Proof. By using the equalities (1.3)–(1.5), and doing the necessary calculations, we will have

    JnJm+Jn+1Jm+1=Jn Jm+Jn+1Jm+1+ε(Jn+1Jm+JnJm+1+Jn+1 Jm+2+Jn+2Jm+1)=19(αn+m+βn+m)19(αnβm+αnβm)αmβmαmβm+ε(16αn+m9+4(αn+mβn+m)3+19(αnβm+αnβm)αmβmαmβm)=19(αn+m+βn+m)19(αnβm+αn βm)αmβm αmβm+ε19(2n+m+4+12Jn+m+2m(1)mjnm)=19(jn+mαmβmjnm)+ε19(2n+m+4+12Jn+m+2m(1)mjnm).

    Theorem 3. (Binet formulas) For every positive integer n, the following equalities hold

    Jn=α_αnβ_βn3, (2.1)

    and

    jn=α_αn+β_βn (2.2)

    where

    α_=1+εα and β_=1+εβ. (2.3)

    Proof. By using the Binet formula for dual Jacobsthal number Jn, we obtain

    Jn=α_αnβ_βn3=(1+εα)2n(1+εβ)(1)n3=2n(1)n+ε(2n+1(1)n+1)3=Jn+Jεn+1.

    If calculations are made similarly for the dual Jacobsthal-Lucas numbers, we obtain

    jn=α_αn+β_βn=(1+εα)2n+(1+εβ)(1)n=jn+εjn+1.

    Theorem 4. (Catalan identity) For the integers n,r such that nr, then Catalan's identity is as follows:

    Jn+rJnrJ2n=(1)n2n9((1)r+12r J2r+ ε(2jr+1)).

    Proof. Using the relation in the equality (1.5), we can write

    Jn+rJnrJ2n=Jn+rJn+rJ2n+ε(  Jn+rJnr+1+Jn+r+1 Jnr2Jn Jn+1).

    From the equalities (1.3) and (1.4), we will have

    Jn+rJn+rJ2n= αn+rβn+(αr   βr3)2=19(1)n+r+12n+r J2r,

    and

    ε(Jn+rJnr+1+Jn+r+1 Jnr2Jn Jn+1)=19αnβn(2αr+1 βr+1)=19(1)n2n(2jr+1);

    we obtain that

    Jn+rJnrJ2n=(1)n2n9((1)r+12r J2r+ ε(2jr+1)).

    Theorem 5. (Cassini identity) For n1, we have

    Jn+rJnrJ2n=(1)n2n9(23ε).

    Proof. If we write r=1 in Theorem 4, the proof is completed.

    Theorem 6. (d'Ocagne's identity) For any integer n and m, we have

    Jm+1JnJmJn+1=(1)m2mJnm(1+ε).

    Proof. From the equality (1.5)

    Jm+1JnJmJn+1=JnJm+1Jn+1Jm+ε(JnJm+2Jn+2Jm). (2.4)

    From the equalities (1.3) and (1.4), and a straightforward computation, we have

    JnJm+1Jn+1Jm=(αnβn3 αm+1βm+13αn+1βn+13αmβm3)αmβmm βm=19αmβm(αnmβnm)=αmβmJnm

    where from the last equality, we will have

    JnJm+1Jn+1 Jm=2m(1)m Jnm (2.5)

    and

    ε(JnJm+2Jn+2Jm)=ε2m(1)m Jnm. (2.6)

    Substituting the equalities (2.5) and (2.6) in (2.4), we obtain

    Jm+1JnJmJn+1=(1)m2mJnm(1+ε).

    In this part, we will give dual Jacobsthal vectors and geometric properties of them.

    A dual Jacobsthal vector in D3 is given by

    Jn=Jn+εJn+1,

    where

    Jn=(Jn,Jn+1,Jn+2) and Jn+1=(Jn+1,Jn+2,Jn+3) (3.1)

    are real vectors in R3.

    Theorem 7. If Jn is a dual unit vector, then

    7(1)n4n+(1)n2n2=0 or jn=7(1)n22n+1.

    Proof. By using the equalities (1.1), (1.3), (1.5) and (3.1), we get the following statements:

    Jn=J2n+J2n+1+J2n+2=(αnβn3)2+(αn+1βn+13)2+(αn+2βn+23)2=21α2n+3β2n+6 αnβn9=7.4n+2n(1)n+13

    and

    Jn,Jn+1=JnJn+1+Jn+1Jn+2+Jn+2Jn+3. (3.2)

    Doing the necessary calculations, we will have

    Jn,Jn+1=7.22n+1(1)njn3.

    Using proposition 1 and above calculations, we easily reach the result.

    Theorem 8. Let Jn and Jm be dual Jacobsthal vectors. The scalar and cross products of Jn and Jm are

    Jn,Jm=73jn+m(1+4ε)+2m(1)m3jnm(1+ε), (3.3)

    and

    Jn×Jm=2n(1)njnm(1+ε)(2e1+e2e3).

    Proof. From the equalities (1.1), (1.4), (1.6) and (3.2),

    Jn,Jm= JnJm+Jn+1Jm+1+Jn+2Jm+2+ε(JnJm+1+JmJn+1+Jn+1Jm+2+Jn+2Jm+1+Jm+3Jn+2+Jn+3Jm+2).

    By doing the necessary calculations, we obtain

    =JnJm+Jn+1Jm+1+Jn+2Jm+2=73(αn+m+βn+m)+αmβm9(1+αβ+α2β2)(αnm+βnm)=73jn+m+2m(1)m3jnm

    and

    JnJm+1+JmJn+1+Jn+1Jm+2+Jn+2Jm+1+Jm+3Jn+2+Jn+3Jm+2=283(αn+m+βn+m)19(α+β)(1+αβ+  α2β2)(αnβm+αmβn)=283(αn+m+βn+m)19(α+β)(1+αβ+  α2β2)(αnβm+αmβn)αmβmαmβm.

    In the last equality, we take into account that α=2 and β=1; thus, we obtain

    =283jn+m2m(1)m3jnm.

    From the equalities (1.2), (1.3), (1.5) and (1.6), we obtain

    Jn×Jm=Jn×Jm+ε(Jn×Jm+1+Jn+1×Jm). (3.4)

    We compute the following expressions:

    Jn×Jm=[e1e2e3JnJn+1Jn+2JmJm+1Jm+2]=(1)m2mJnm(2e1e2+e3). (3.5)

    In the equality (3.4), if the dual part is calculated similarly, then

    Jn×Jm+1+Jn+1×Jm=(1)m2mJnm(2e1e2+e3). (3.6)

    Substituting the equalities (3.5) and (3.6) in (3.4), we obtain

    Jn×Jm=(1)m2mJnm(2e1e2+e3)(1+ε).

    Proposition 2. (E. Study mapping) Let U= u+εu be the unit dual vector corresponding to the directed line l in R3. The unit real vector u is the direction vector of the line l, and the real vector u determines the position of l [2] (see Figure 1).

    Figure 1.  E. Study mapping.

    Proof. Let us consider a dual unit vector U=u+εu. The directed line corresponding with U is in the direction of u according to the E. Study mapping; let P,X be points on the line and the origin be considered as the point O. Then, the line equation is given by

    OX=OP+ru,

    where rIR is a parameter. A point P is on the line of vectors u,u if and only if

    u×u= u×(OP×u),

    and then

    OP=u×u+u,OPu,

    and

    OX=u×u+(u,OP+r)u.

    By taking a new parameter t=u,OP +r and OX=x, we will have the result as

    x=u×u+tu. (3.7)

    Theorem 9. If J0n is a dual Jacobsthal vector and its unitized vector of J0n is Jn=Jn+  εJn+1, whose terminal point is on the dual unit sphere, then the equation of the oriented line that corresponds to Jn in R3 is given by

    xn=(1)n2n(29+tJn)e1+(tJn+1)e2+819+tJn+2)e3),

    where tIR is a parameter.

    Proof. By using the equalities (1.2), (1.3), (1.5) and (3.6), we obtain the equation of the oriented line which corresponds with Jn as follows:

    xn=Jn×Jn+1+tJn,=[e1e2e3JnJn+1Jn+2JmJm+1Jm+2]+t(Jne1+Jn+1e2+Jn+2e3)=(1)n2n(29+tJn)e1+(tJn+1)e2+(19+tJn+2)e3).

    Definition 1. (Dual angle)The dual angle represents the relative displacement and orientation between two lines d1 and d2 in D3. The dual angle is defined as

    φ=θ+εθ.

    This concept was given by Study in 1903. θ the primary component of θ is the projected angle between d1 and d2, and θ is the shortest distance between lines d1 and d2 (see Figure 2).

    Figure 2.  Dual angle.

    The scalar product of any unit dual vectors U= u+εu and V=v+ εv is obtained as follows:

    U,V=cos φ=cosθ εθsinθ, (3.8)

    where φ=θ+εθ is a dual angle [2].

    Theorem 10. From equalities (3.3) and (3.8), the scalar product of Jn and Jm is

    Jn,Jm=7jn+m+2m(1)mjnm3+ε28jn+m+2m(1)mjnm3,=cosφ=cosθ εθsinθ.

    In the last the equality, φ is a dual angle if and only if the following cases are true.

    Case 1. If cosθ = 0 and θ 0, then

    Jn,Jm=cosφ= εθ,

    where

    28jn+m+2m(1)mjnm3=θ.

    Therefore, lines Jn and Jm are perpendicular but not intersecting.

    Case 2. If θ = 0, then

    Jn,Jm=cosφ=cosθ=7jn+m+2m(1)mjnm3θ=cos1(7jn+m+2m(1)mjnm3),

    lines Jn and Jm are intersecting.

    Case 3. If θ = π2 and θ = 0, then

    Jn,Jm=cosφ=cosπ2=7jn+m+2m(1)mjnm3,

    the last equality is

    jn+mjnm=2m(1)m+17,

    and lines Jn and Jm are perpendicular and intersecting.

    Case 4. If θ = 0, then

    cosφ=1,ε=3722n+1(1)njn28j2n+12n(1)n.

    Thus, lines Jn and Jm are parallel.

    In this study, the dual Jacobsthal numbers and the dual Jacobsthal-Lucas numbers with coefficients of dual numbers have been introduced. We obtained some fundamental identities such as the generating function, the Binet formulas, the Cassini's, Catalan's and d'Ocagne identities for these numbers. In addition, some properties of dual Jacobsthal vectors to exert in geometry of dual space are obtain.

    The authors declare they have not used Artificial Intelligence (AI) tools in the creation of this article.

    The author would like to express their sincere thanks to the editor and the anonymous reviewers for their helpful comments and suggestions.

    There are no competing interests.



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