International Journal of Pure and Applied Mathematics ————————————————————————– Volume 34 No
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International Journal of Pure and Applied Mathematics ————————————————————————– Volume 34 No. 2 2007, 267-278 GENERATING MATRICES FOR FIBONACCI, LUCAS AND SPECIAL ORTHOGONAL POLYNOMIALS WITH ALGORITHMS 1 2 3 Mustafa A¸sci §, Bayram C¸ekım , Dursun Ta¸sci 1,2,3Department of Mathematics Faculty of Sciences and Arts University of Gazi Teknikokullar, Ankara, 06500, TURKEY 1e-mail: [email protected] 2e-mail: [email protected] 3e-mail: [email protected] Abstract: In this paper we get the Fibonacci polynomials for special cases of Sturm Liouville boundary value problems. We show the orthogonallity of Fibonacci polynomials. In Section 3 by using the definition of n n Hessenberg × matrices we give the generating matrices of the Fiboniacci and Lucas polyno- mials and for the special orthogonal polynomials. In the last section we give two algorithms for finding the Fibonacci and Lucas polynomials. AMS Subject Classification: 15A15, 11B39, 15A36 Key Words: Fibonacci polynomial, Sturm Liouville algorithm 1. Introduction The Fibonacci sequence, Fn , is defined by the recurrence relation, for n 1 { } ≥ Fn+1 = Fn + Fn 1 , (1.1) − where F = F = 1. The Lucas sequence, Ln , is defined by the recurrence 0 1 { } Received: November 2, 2006 c 2007, Academic Publications Ltd. §Correspondence author 268 M. A¸sci, B. C¸ekım, D. Ta¸sci relation, for n 1 ≥ Ln+1 = Ln + Ln 1 , (1.2) − where L0 = 2, L1 = 1. Large classes of polynomials can be defined by Fibonacci-like recurrence relation, and yield Fibonacci numbers. Such polynomials, called the Fibonacci polynomials, were studied in 1883 by the Belgian mathematician Eugene Charles Catalan and the German mathematician E. Jacobsthal. The polynomials fn(x) studied by Catalan are defined by the recurrence relation fn(x)= xfn 1(x)+ fn 2(x) , (1.3) − − where f (x) = 1, f (x)= x, and n 3. The Fibonacci polynomials studied by 1 2 ≥ Jacobsthal were defined by Jn(x)= Jn 1(x)+ xJn 2(x) , (1.4) − − where J1(x)=1= J2(x). Lucas polynomials Ln(x), originally studied in 1970 by Bicknell, are defined by Ln(x)= xLn 1(x)+ Ln 2(x) , (1.5) − − where L (x) = 2, L (x)= x and n 2. 0 1 ≥ A differential equation defined on the interval a x b having the form ≤ ≤ of d dy p(x) + [q(x)+ λr(x)] y = 0 dx dx and the boundary conditions a1y(a)+ a2y′(a) = 0 , b1y(b)+ b2y′(b) = 0 , is called as Sturm-Liouville boundary value problem or Sturm-Liouville system where p(x) > 0, q(x), the weighting function r(x) > 0 are given functions; a1, a2, b1, b2 are given constants; and the eigenvalue λ is an unspecified param- eter. For a = 1, b = 1, p(x) = √1 x2, q(x) = 0, r(x) = 1 and λ = n2 − − √1 x2 the Sturm-Liouville equation becomes the Chebyshev’s differential− equation 2 2 (1 x )y′′ xy′ + n y = 0 , − − which is defined on 1 <x< 1. The solutions of the Chebyshev’s differential − equation with n = 0, 1, 2, 3, ... is called Chebyshev polynomials Tn(x) which GENERATING MATRICES FOR FIBONACCI... 269 form a complete orthogonal set on the interval 1 <x< 1 with respect to − r(x)= 1 √1 x2 − −x2 −x2 For a = , b = , p(x)= e 2 , q(x) = 0, r(x)= e 2 and λ = 2n the −∞ ∞ Sturm-Liouville equation becomes the Hermite’s differential equation y′′ 2xy′ + 2ny = 0 , − which is defined on <x< . The solutions of the Hermite’s differential −∞ ∞ equation with n = 0, 1, 2, 3, ... is called Hermite polynomials Hn(x) which form a complete orthogonal set on the interval <x< with respect to r(x)= −x2 −∞ ∞ e 2 We can get Legendre polynomials, Bessel functions, Laguerre polynomials for some special cases of the Sturm-Liouville boundary value problem. 2. Computations on Fibonacci Differential Equation The ordinary differential equation 2 (x + 4)y′′ + 3xy′ + λy = 0 (2.1) is known as Fibonacci differential equation. When we solve the equation the solutions are the Fibonacci polynomials. Let us show that the eigenvalue λ is (1 n2): − ∞ n By the serial solution of ODE, suppose that y = anx then y′ = n=0 ∞ n 1 ∞ n 2 nanx − and y′′ = n(n 1)anx − . n=0 n=0 − Substituting these values in (2.1) 2 ∞ n 2 ∞ n 1 ∞ n (x + 4) n(n 1)anx − + 3x nanx − + λ anx = 0 , − n=0 n=0 n=0 ∞ n ∞ n 2 ∞ n 1 n(n 1)anx + 4 n(n 1)anx − + 3x nanx − − − n=0 n=2 n=0 ∞ n + λ anx = 0 , n=0 ∞ n ∞ n ∞ n n(n 1)anx + 4 (n + 1)(n + 2)an x + 3 nanx − +2 n=0 n=0 n=0 270 M. A¸sci, B. C¸ekım, D. Ta¸sci ∞ n + λ anx = 0 , n=0 ∞ n (n(n 1)an + 4(n + 1)(n + 2)an + 3nan + λan)x = 0 . − +2 n=0 For this solution we get (n2 + 2n + λ) an = − an , n 0 , +2 4(n + 1)(n + 2) ≥ or (n2 1+ λ) an+1 = − − an 1 , n 1 , 4n(n + 1) − ≥ then we get λ = 1 n2 − When we get λ = 1 n2 the solutions of the ODE (x2 + 4)y + 3xy + (1 − ′′ ′ − n2)y = 0 are the Fibonacci polynomials. Now we show that Fibonacci polynomials are orthogonal with respect to the weight function √2 x2 + 4. Theorem 1. Let Fn and Fm be Fibonacci polynomials as defined in (1.3). Then we get 2i 2 2 0, m = n , x + 4FmFndx = n+1 2i ( 1) 2iπ, m = n . − − Proof. Case 1. m = n. Since Fm and Fn are the solutions of ODE (2.1) 2 2 (x + 4)F ′′ + 3xF ′ + (1 n )Fn = 0 . n n − 2 2 In this equation product this equation with √x + 4Fm 2 2 (x + 4)F ′′ + 3xF ′ + (1 n )Fm = 0 m m − 2 2 multiply this equation with √x + 4Fn 3 2 2 2 2 2 2 2 (x + 4) F ′′Fm + 3x x + 4FmF ′ + (1 n ) x + 4FmFn = 0 , (2.2) n n − 3 2 2 2 2 2 2 2 (x + 4) Fm′′ Fn + 3x x + 4FnFm′ + (1 m ) x + 4FmFn = 0 . (2.3) − Subtract (2.2) and (2.3) we get 3 2 2 2 2 (x + 4) F ′′Fm F ′′ Fn + 3x x + 4 FmF ′ FnF ′ n − m n − m GENERATING MATRICES FOR FIBONACCI... 271 2 2 2 2 x + 4FmFn(n m ) = 0 , − − d 3 2 2 2 2 2 2 (x + 4) FmF ′ FnF ′ = x + 4FmFn(n m ) . dx n − m − Integrate this equations from 2i to 2i − 2i 2i d 3 2 2 2 2 2 2 (x + 4) FmFn′ FnFm′ dx = (n m ) x + 4FmFndx , 2i dx − − 2i − − 2i 3 2i 2 2 2 2 2 2 (x + 4) FmFn′ FnFm′ = (n m ) x + 4FmFndx , − 2i − 2i − − 2i 2 2 2 2 (n m ) x + 4FmFndx = 0 , − 2i − when n = m we get 2i 2 2 x + 4FmFndx = 0 . 2i − Case 2. m = n. This case is computed by a short MATLAB algorithm easily. 3. Generating Matrices for Fibonacci, Lucas Polynomials and Special Functions A lower Hessenberg matrix, A, is an n n matrix, where aj,k = 0 whenever × k > j +1 and aj,j = 0 for some j. That is, all entries above the superdiagonal +1 are 0 but the matrix is not lower triangular. Throughout this paper we will refer to the following lower Hessenberg matrix m1,1 m1,2 0 ... ... 0 .. .. m2,1 m2,2 m2,3 . 0 .. .. m , m , m , . 0 M = 3 1 3 2 3 3 . (3.1) n . . .. .. .. 0 . .. .. .. . mn 1,n − mn,1 mn,2 ... ... mn,n 1 mn,n − We will consider the sequence det Mn,n 1 . Our result is stated in the { ≥ } following theorem. 272 M. A¸sci, B. C¸ekım, D. Ta¸sci Theorem 2. Let Mn be as above for all n 1 and define det M = 1 ≥ 0 Then det Mn,n 0 satisfies: { ≥ } det M0 = 1, det M1 = m1,1 and n 1 n 1 − n r − det Mn = mn,n. det Mn 1 + ( 1) − mn,r mj,j+1. det Mr 1 , − − − r=1 j=r n 2. ≥ Proof. It is proved in [2]. We can obtain the family of matrices Fn by letting mj,j = 1 and mj,j = { } +1 mj ,j = i = √ 1, 1 j n 1 in the above theorem. Then det M = 1, +1 − ≤ ≤ − 1 det M2 = 2 and det Mn = det Mn 1 + det Mn 2, which is exactly the Fibonacci − − recurrence. By using above theorem we get the following results by determinant com- putations. Corollary 1. Let Fn be the n n Hessenberg matrix defined as in (3.1). × For special cases as below we get det Fn = Fn(x) 1 0 0 ... ... 0 . 0 x i 0 .. 0 . 0 i x i .. 0 Fn = , .. .. 0 0 i . 0 . .. .. .. . i 0 0 ... 0 i x where Fn(x) is the n-th Fibonacci polynomial. Corollary 2. Let Ln be the n n Hessenberg matrix defined as in (3.1). × For special cases as below we get det Ln = Ln(x) 2 0 0 ... ... 0 . x .. 0 2 i 0 0 . 0 i x i .. 0 Ln = , .. .. 0 0 i . 0 . .. .. .. . i 0 0 ... 0 i x GENERATING MATRICES FOR FIBONACCI... 273 where Ln(x) is the n-th Lucas polynomial. Corollary 3. Let Hn be the n n Hessenberg matrix defined as in (3.1). × For m , = 1, mi,i = 2x, i = 1, mi,i = √2i, and mi ,i = (n 2)√2i.