On the recursive sequence x(n+1)=xn-(k+1)/1+xnxn-1...xn-k

In this paper a solution of the one difference equation was investigated.

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Hauptverfasser: Simsek, D., Abdullayev, F.G.
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Veröffentlicht: Інститут прикладної математики і механіки НАН України 2017
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spelling irk-123456789-1693782020-06-12T01:26:20Z On the recursive sequence x(n+1)=xn-(k+1)/1+xnxn-1...xn-k Simsek, D. Abdullayev, F.G. In this paper a solution of the one difference equation was investigated. 2017 Article On the recursive sequence x(n+1)=xn-(k+1)/1+xnxn-1...xn-k / D. Simsek, F.G. Abdullayev // Український математичний вісник. — 2017. — Т. 14, № 4. — С. 564-574. — Бібліогр.: 28 назв. — англ. 1810-3200 http://dspace.nbuv.gov.ua/handle/123456789/169378 en Український математичний вісник Інститут прикладної математики і механіки НАН України
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
language English
description In this paper a solution of the one difference equation was investigated.
format Article
author Simsek, D.
Abdullayev, F.G.
spellingShingle Simsek, D.
Abdullayev, F.G.
On the recursive sequence x(n+1)=xn-(k+1)/1+xnxn-1...xn-k
Український математичний вісник
author_facet Simsek, D.
Abdullayev, F.G.
author_sort Simsek, D.
title On the recursive sequence x(n+1)=xn-(k+1)/1+xnxn-1...xn-k
title_short On the recursive sequence x(n+1)=xn-(k+1)/1+xnxn-1...xn-k
title_full On the recursive sequence x(n+1)=xn-(k+1)/1+xnxn-1...xn-k
title_fullStr On the recursive sequence x(n+1)=xn-(k+1)/1+xnxn-1...xn-k
title_full_unstemmed On the recursive sequence x(n+1)=xn-(k+1)/1+xnxn-1...xn-k
title_sort on the recursive sequence x(n+1)=xn-(k+1)/1+xnxn-1...xn-k
publisher Інститут прикладної математики і механіки НАН України
publishDate 2017
url http://dspace.nbuv.gov.ua/handle/123456789/169378
citation_txt On the recursive sequence x(n+1)=xn-(k+1)/1+xnxn-1...xn-k / D. Simsek, F.G. Abdullayev // Український математичний вісник. — 2017. — Т. 14, № 4. — С. 564-574. — Бібліогр.: 28 назв. — англ.
series Український математичний вісник
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fulltext Український математичний вiсник Том 14 (2017), № 4, 564 – 574 On the recursive sequence xn+1 = xn−(k+1) 1+xnxn−1...xn−k Dağıstan Simsek, Fahreddin G. Abdullayev Abstract. In this paper a solution of the following difference equation was investigated xn+1 = xn−(k+1) 1 + xnxn−1...xn−k , n = 0, 1, 2, . . . where x−(k+1), x−k, . . . , x−1, x0 ∈ (0,∞) and k = 0, 1, 2, . . . . Key words and phrases. Difference equation, period k + 2 solution. 1. Introduction The study of difference equations has been growing continuously for the last decade. This is largely due to the fact that difference equations manifest themselves as mathematical models describing real life situations in probability theory, queuing theory, statistical problems, stochastic time series, combinatorial analysis, number theory, geometry, electrical net- work, quanta in radiation, genetics in biology, economics, psychology, sociology, etc. In fact, now it occupies a central position in applicable analysis and will no doubt continue to play an important role in mathe- matics as a whole. Recently there has been a lot of interest in studying the periodic nature of nonlinear difference equations. For some recent results, concerning among other problems, the periodic nature of scalar nonlinear difference equations see, for example, [1–28]. Cinar [2, 3, 4] has studied the following problems with positive initial values xn+1 = xn−1 1 + axnxn−1 , xn+1 = xn−1 −1 + axnxn−1 , Received 19.12.2017 ISSN 1810 – 3200. c⃝ Iнститут прикладної математики i механiки НАН України D. Simsek, F. G. Abdullayev 565 xn+1 = axn−1 1 + bxnxn−1 for n = 0, 1, 2, ..., respectively. In [18] Stevic solved the following problem xn+1 = xn−1 1 + xn for n = 0, 1, 2, . . . , where x−1, x0 ∈ (0,∞). Also, this result was generalized to the equation of the following form: xn+1 = xn−1 g(xn) for n = 0, 1, 2, . . . , where x−1, x0 ∈ (0,∞). Simsek et al. [19, 20, 21, 24], studied the following problems with positive initial values xn+1 = xn−3 1 + xn−1 , xn+1 = xn−5 1 + xn−2 , xn+1 = xn−5 1 + xn−1xn−3 , xn+1 = xn−3 1 + xnxn−1xn−2 , for n = 0, 1, 2, . . . , respectively. In this paper we investigate the following nonlinear difference equation xn+1 = xn−(k+1) 1 + xnxn−1...xn−k for n = 0, 1, 2, . . . (1.1) where x−(k+1), x−k, ..., x−1, x0 ∈ (0,∞) and k = 0, 1, 2, . . . . 2. Main result Theorem 1. Consider the difference equation (1.1). Then the following statements are true. a) The sequences (x(k+2)n−(k+1)), (x(k+2)n−k), . . . , (x(k+2)n) are de- creasing and there exist a1, a2, . . . , ak+2 > 0 such that lim n→∞ x(k+2)n−(k+1) = a1, lim n→∞ x(k+2)n−k = a2, . . . , lim n→∞ x(k+2)n = ak+2. 566 On the recursive sequence . . . b) (a1, a2, . . . , ak+2, a1, a2, . . . , ak+2, . . .) is a solution of equation (1.1) of period k+2. c) a1 × a2 × . . .× ak+2 = 0. d) If there exists n0 ∈ N such that xn−k ≥ xn+1 for all n > n0, then lim n→∞ xn = 0. e) The following formulas x(k+2)n+1 = x−(k+1) ( 1− x0x−1...x−k 1+x0x−1...x−k n∑ j=0 (k+2)j∏ i=1 1 1+xixi−1...xi−k ) , . . . x(k+2)n+k+2 = x0 ( 1− x−1x−2...x−(k+1) 1+x0x−1...x−k n∑ j=0 (k+2)j+(k+1)∏ i=1 1 1+xixi−1...xi−k ) holds. f) If x(k+2)n+1 → a1 ̸= 0, x(k+2)n+2 → a2 ̸= 0,..., x(k+2)n+k+1 → ak+1 ̸= 0 then x(k+2)n+k+2 → 0 as n→ ∞. Proof. a) Firstly, from the equation (1.1), we obtain xn+1(1 + xnxn−1...xn−k) = xn−(k+1). If xn, xn−1, ..., xn−k ∈ (0,+∞), then (1 + xnxn−1...xn−k) ∈ (1,+∞). Since xn+1 < xn−(k+1), n ∈ N , we obtain that lim n→∞ x(k+2)n−(k+1) = a1, lim n→∞ x(k+2)n−(k) = a2, ..., lim n→∞ x(k+2)n = ak+2. b) (a1, a2, ..., ak+2, a1, a2, ..., ak+2, ...) is a solution of equation (1.1) of period k + 2. c) In view of the equation (1.1), we obtain: x(k+2)n+1 = x(k+2)n−(k+1) 1 + x(k+2)n...x(k+2)n−k . Taking limit as n→ ∞ on both sides of the above equality, we get: lim n→∞ x(k+2)n+1 = lim n→∞ x(k+2)n−(k+1) 1 + x(k+2)n...x(k+2)n−k , D. Simsek, F. G. Abdullayev 567( lim n→∞ x(k+2)n−(k+1) ) × ( lim n→∞ x(k+2)n−(k) ) × ...× ( lim n→∞ x(k+2)n ) = 0. Then a1 × a2 × ...× ak+2 = 0. d) If there exists n0 ∈ N such that xn−k ≥ xn+1 for all n > n0, then a1 ≤ a2 ≤ ... ≤ ak+2 ≤ a1. Since a1 × a2 × ...× ak+2 = 0, we obtain the result. e) Subracting xn−(k+1) from the left and right-hand sides of equation (1.1), we obtain: xn+1 − xn−(k+1) = 1 1 + xnx−1...xn−k (xn − xn−(k+2)) and for n > 1 the following formula xn − xn−(k+2) = (x1 − x−(k+1)) n−1∏ i=1 1 1 + xixi−1...xi−k (2.1) holds. Replacing n by (k+2)j in (2.1) and summing from j = 0 to j = n, we obtain: x(k+2)n+1 − x−(k+1) = (x1 − x−(k+1)) n∑ j=0 (k+2)j∏ i=1 1 1 + xixi−1...xi−k , (n = 0, 1, 2, ...), . (2.2) . . Also, replacing n by (k + 2)j + (k + 1) in (2.1) and summing from j = 0 to j = n, we obtain: x(k+2)n+k+2 − x0 = (xk+1 − x0) n∑ j=0 (k+2)j+(k+1)∏ i=1 1 1 + xixi−1...xi−k , (n = 0, 1, 2, ...). From the formulas above, we obtain: 568 On the recursive sequence . . . x(k+2)n+1 = x−(k+1) ( 1− x0x−1...x−k 1+x0x−1...x−k n∑ j=0 (k+2)j∏ i=1 1 1+xixi−1...xi−k ) , . . . x(k+2)n+k+2 = x0(1− x−1x−2...x−(k+1) 1+x0x−1...x−k n∑ j=0 (k+2)j+(k+1)∏ i=1 1 1+xixi−1...xi−k ) . . . (2.3) f) Suppose that a1 = a2 = ... = ak+2 = 0. By (e) we have: lim n→∞ x(k+2)n+1 = lim n→∞ x−(k+1) ( 1− x0x−1...x−k 1+x0x−1...x−k n∑ j=0 (k+2)j∏ i=1 1 1+xixi−1...xi−k ) , a1 = x−(k+1) 1− x0x−1...x−k 1 + x0x−1...x−k ∞∑ j=0 (k+2)j∏ i=1 1 1 + xixi−1...xi−k  , a1 = 0 ⇒ 1 + x0x−1...x−k x0x−1...x−k = ∞∑ j=0 (k+2)j∏ i=1 1 1 + xixi−1...xi−k . (2.4) Similarly, lim n→∞ x(k+2)n+2 = lim n→∞ x−(k)(1− x0x−1...x−(k+1) 1+x0x−1...x−k n∑ j=0 (k+2)j+1∏ i=1 1 1+xixi−1...xi−k ), a2 = x−(k)(1− x0x−1...x−(k+1) 1 + x0x−1...x−k ∞∑ j=0 (k+2)j+1∏ i=1 1 1 + xixi−1...xi−k ), a2 = 0 ⇒ 1+x0x−1...x−k x0x−1...x−(k+1) = ∞∑ j=0 (k+2)j+1∏ i=1 1 1+xixi−1...xi−k , . . . (2.5) D. Simsek, F. G. Abdullayev 569 Similarly, lim n→∞ x(k+2)n+k+1= lim n→∞ x−1 ( 1− x0x−2x−3...x−(k+1) 1+x0x−1...x−k n∑ j=0 (k+2)j+k∏ i=1 1 1+xixi−1...xi−k ) , ak+1 = x−1 1− x0x−2x−3...x−(k+1) 1 + x0x−1...x−k ∞∑ j=0 (k+2)j+k∏ i=1 1 1 + xixi−1...xi−k  , ak+1 = 0 ⇒ 1 + x0x−1...x−k x−2x−3...x−(k+1) = ∞∑ j=0 (k+2)j+k∏ i=1 1 1 + xixi−1...xi−k . (2.6) lim n→∞ x(k+2)n+k+2= lim n→∞ x0 ( 1− x−1x−2...x−(k+1) 1+x0x−1...x−k n∑ j=0 (k+2)j+(k+1)∏ i=1 1 1+xixi−1...xi−k ) , ak+2 = x0 1− x−1x−2...x−(k+1) 1 + x0x−1...x−k ∞∑ j=0 (k+2)j+(k+1)∏ i=1 1 1 + xixi−1...xi−k  , ak+2 = 0 ⇒ 1 + x0x−1...x−k x−1x−2...x−(k+1) = ∞∑ j=0 (k+2)j+(k+1)∏ i=1 1 1 + xixi−1...xi−k . (2.7) From (2.4) and (2.5), we get: 1 + x0x−1...x−k x0x−1...x−k > 1 + x0x−1...x−k x0x−1...x−(k+1) , thus x−(k+1) > x−k, and . . . Therefore, from (2.6) and (2.7), we have: 1 + x0x−1...x−k x0x−2...x−(k+1) > 1 + x0x−1...x−k x−1x−2...x−(k+2) , thus, x−1 > x0. From here we obtain x−(k+1) > x−k > ... > x−1 > x0. We arrive at a contradiction which completes the proof of theorem. 570 On the recursive sequence . . . 3. Examples Consider the following equation xn+1 = xn−3 1+xnxn−1xn−2 which is a special case of (1.1) for k = 2. Example 1. If the initial conditions are selected as follows: x[−3] = 0.99999; x[−2] = 0.99998; x[−1] = 0.99997; x[0] = 0.99996. The follow- ing solutions are obtained: x(n) = {0.500018, 0.666661, 0.74998, 0.799968, 0.357163, 0.549016, 0.648287, 0.709744, 0.285135, 0.485341, 0.590307, 0.656143, 0.240015, 0.44406, 0.551724, 0.619703, 0.208378, 0.414527, 0.523691, 0.592883, 0.184617, 0.392054, 0.502143, 0.572091, 0.165929, 0.374216, 0.484917, 0.555368, 0.150738, 0.359617, 0.470745, 0.541549, 0.138079, 0.347389, 0.458826, 0.529887, 0.127325, 0.336958, 0.448627, 0.519881, 0.118048, 0.327929, 0.439777, 0.511178, 0.109943, 0.32002, 0.432007, 0.503525, 0.102788, 0.313021, 0.42512, 0.49673, 0.0964144, 0.306775, 0.418964, 0.49065, 0.090695, 0.30116, 0.413424, 0.485172, 0.0855285, 0.296081, 0.408406, 0.480205, 0.0808346, 0.291461, 0.403837, 0.475679, 0.0765488, 0.287237, 0.399657, 0.471536, 0.0726179, 0.283359, 0.395817, 0.467726, 0.0689983, 0.279785, 0.392275, 0.464211, 0.0656534, 0.27648, 0.388997, 0.460956, 0.0625523, 0.273413, 0.385954, 0.457933, 0.0596689, 0.27056, 0.383122, 0.455118, 0.0569808, 0.267898, 0.380478, 0.45249, 0.0544686, 0.265409, 0.378006, 0.450031, 0.0521156, 0.263077, 0.375688, 0.447725, 0.0499071, 0.260887, 0.37351, 0.445558, 0.0478305, 0.258826, 0.371461, 0.443519, 0.0458743, 0.256885, 0.36953, 0.441596, 0.0440287, 0.255052, 0.367707, 0.43978, 0.0422847, 0.25332, 0.365983, 0.438062, 0.0406344, 0.251681, 0.36435, 0.436436, 0.0390707, 0.250127, 0.362803, 0.434894, 0.0375873, 0.248652, 0.361334, 0.43343, . . .}. The limits of solutions approaching zero due to the fact that the initial condition is selected. The graph of the solutions is given below: Example 2. If the initial conditions are selected as follows: x[−3] = 0.1; x[−2] = 0.09; x[−1] = 0.08; x[0] = 0.07; The following solutions D. Simsek, F. G. Abdullayev 571 Figure 3.1. x(n) graph of the solutions. are obtained: x(n) = {0.0999496, 0.0899497, 0.0799497, 0.0699497, 0.0998994, 0.0898994, 0.0798995, 0.0698996, 0.0998492, 0.0898493, 0.0798494, 0.0698495, 0.0997992, 0.0897993, 0.0797995, 0.0697996, 0.0997493, 0.0897495, 0.0797496, 0.0697498, 0.0996996, 0.0896997, 0.0796999, 0.0697001, 0.0996499, 0.0896501, 0.0796503, 0.0696506, 0.0996004, 0.0896006, 0.0796008, 0.0696011, 0.099551, 0.0895512, 0.0795515, 0.0695518, 0.0995017, 0.0895019, 0.0795022, 0.0695026, 0.0994525, 0.0894528, 0.0794531, 0.0694535, 0.0994034, 0.0894037, 0.0794041, 0.0694045, 0.0993544, 0.0893548, 0.0793552, 0.0693557, 0.0993056, 0.089306, 0.0793064, 0.0693069, 0.0992569, 0.0892573, 0.0792578, 0.0692583, 0.0992083, 0.0892087, 0.0792092, 0.0692098, 0.0991598, 0.0891602, 0.0791608, 0.0691614, 0.0991114, 0.0891119, 0.0791124, 0.0691131, 0.0990631, 0.0890637, 0.0790642, 0.0690649, 0.099015, 0.0890155, 0.0790161, 0.0690168, 0.0989669, 0.0889675, 0.0789681, 0.0689689, 0.098919, 0.0889196, 0.0789203, 0.068921, 0.0988712, 0.0888718, 0.0788725, 0.0688733, 0.0988235, 0.0888241, 0.0788248, 0.0688257, 0.0987759, 0.0887766, 0.0787773, 0.0687782, 0.0987284, 0.0887291, 0.0787299, 0.0687308, 0.098681, 0.0886817, 0.0786825, 0.0686835, 0.0986337, 0.0886345, 0.0786353, 0.0686363, 0.0985866, 0.0885874, 0.0785882, 0.0685892, 0.0985395, 0.0885403, 0.0785412, 0.0685422, 0.0984926, 0.0884934, 0.0784943, 0.0684954, 0.0984457, 0.0884466, 0.0784475, 0.0684486, 0.098399, 0.0883999, 0.0784009, 0.068402, 0.0983524, 0.0883533, 0.0783543, 0.0683554, . . .}. In this case the limits of solutions are not approaching zero, since the initial condition are hasn’t satisfied. The graph of the solutions is given below: 572 On the recursive sequence . . . Figure 3.2. x(n) graph of the solutions. References [1] A. M. Amleh, E. A. Grove, G. Ladas, D. A. Georgiou, On the recursive sequence yn+1 = α + yn−1 yn // J. Math. Anal. Appl., 233 (1999), 790–798. [2] C. Cinar, On the positive solutions of the difference equation xn+1 = xn−1 1+axnxn−1 // Appl. Math. Comp., 158 (2004), No. 3, 809–812. [3] C. Cinar, On the positive solutions of the difference equation xn+1 = xn−1 −1+axnxn−1 // Appl. Math. Comp., 158 (2004), No. 3, 793–797. [4] C. Cinar, On the positive solutions of the difference equation xn+1 = axn−1 1+bxnxn−1 // Appl. Math. Comp., 156 (2004), No. 3, 587–590. [5] E. M. Elabbasy, H. El-Metwally, E. M. Elsayed, On the difference equation xn+1 = axn − bxn cxn−dxn−1 // Advances in Difference Equation, 2006 (2006), 1–10. [6] E. M. Elabbasy, H. 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Simsek, F.Abdullayev, On The Recursive Sequence xn+1 = xn−(4k+3) 1+ 2∏ t=0 xn−(k+1)t−k // Ukrainian Mathematical Bulletin, 13 (2016), No. 3, 376–387. [26] I. Yalcinkaya, B. D. Iricanin, C. Cinar, On a max-type difference equation // Discrete Dynamics in Nature and Society, 2007 (2007), doi: 1155/2007/47264, 1–10. [27] H. D. Voulov, Periodic solutions to a difference equation with maximum // Proc. Am. Math. Soc., 131 (2002), No. 7, 2155–2160. 574 On the recursive sequence . . . [28] X. Yang, B. Chen, G. M. Megson, D. J. Evans, Global attractivity in a recursive sequence // Applied Mathematics and Computation, 158 (2004), 667–682. Contact information Dağıstan Simsek Kyrgyz–Turkish Manas University, Bishkek, Kyrgyzstan, Selcuk University, Konya, Turkey E-Mail: dagistan.simsek@manas.edu.kg dsimsek@selcuk.edu.tr Fahreddin G. Abdullayev Kyrgyz–Turkish Manas University, Bishkek, Kyrgyzstan, Mersin University, Mersin, Turkey E-Mail: fabdul@mersin.edu.tr fahreddin.abdullayev@manas.edu.kg