Dividend payments in a perturbed compound Poisson model with stochastic investment and debit interest

UDC 519.21 We consider a compound Poisson insurance risk model perturbed by diffusion with stochastic return on investment and debit interest. If the initial surplus is nonnegative, then the insurance company can invest its surplus in a risky asset and risk-free asset based on a fixed proportion....

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Datum:2019
Hauptverfasser: Li, Y. F., Lu, Y. H., Лі, Я. Ф., Лю, Я. Х.
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Sprache:Englisch
Veröffentlicht: Institute of Mathematics, NAS of Ukraine 2019
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Ukrains’kyi Matematychnyi Zhurnal
_version_ 1860507240311554048
author Li, Y. F.
Lu, Y. H.
Лі, Я. Ф.
Лю, Я. Х.
author_facet Li, Y. F.
Lu, Y. H.
Лі, Я. Ф.
Лю, Я. Х.
author_sort Li, Y. F.
baseUrl_str https://umj.imath.kiev.ua/index.php/umj/oai
collection OJS
datestamp_date 2019-12-05T08:56:08Z
description UDC 519.21 We consider a compound Poisson insurance risk model perturbed by diffusion with stochastic return on investment and debit interest. If the initial surplus is nonnegative, then the insurance company can invest its surplus in a risky asset and risk-free asset based on a fixed proportion. Otherwise, the insurance company can get the business loan when the surplus is negative. The integrodifferential equations for the moment generating function of the cumulative dividends value are obtained under the barrier and threshold dividend strategies, respectively. The closed-form of the expected dividend value is obtained when the claim amount is exponentially distributed.
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fulltext UDC 519.21 Y. H. Lu, Y. F. Li (School Statist., Qufu Normal Univ., Shandong, China) DIVIDEND PAYMENTS IN A PERTURBED COMPOUND POISSON MODEL WITH STOCHASTIC INVESTMENT AND DEBIT INTEREST* ДИВIДЕНДНI ВИПЛАТИ У ЗБУРЕНIЙ СКЛАДНIЙ ПУАССОНIВСЬКIЙ МОДЕЛI ЗI СТОХАСТИЧНИМИ IНВЕСТИЦIЯМИ ТА ДЕБЕТОВИМИ ВIДСОТКАМИ We consider a compound Poisson insurance risk model perturbed by diffusion with stochastic return on investment and debit interest. If the initial surplus is nonnegative, then the insurance company can invest its surplus in a risky asset and risk-free asset based on a fixed proportion. Otherwise, the insurance company can get the business loan when the surplus is negative. The integrodifferential equations for the moment generating function of the cumulative dividends value are obtained under the barrier and threshold dividend strategies, respectively. The closed-form of the expected dividend value is obtained when the claim amount is exponentially distributed. Розглядається складна пуассонiвська модель страхових ризикiв, збурена дифузiєю, зi стохастичним доходом по iнвестицiях та дебетовим вiдсотком. Якщо початковий надлишок є невiд’ємним, то стрaхова компанiя може вкладати цей надлишок у ризиковi або безризиковi активи в фiксованiй пропорцiї. В протилежному випадку, коли надлишок є вiд’ємним, страхова компанiя може отримувати бiзнесовi кредити. Iнтегро-диференцiальнi рiвняння для функцiї, що породжує моменти значень кумулятивних дивiдендiв, отримано для бар’єрних та порогових дивiдендних стратегiй вiдповiдно. Очiкувану величину дивiдендiв отримано в замкненiй формi у випадку експоненцiального розподiлу суми позову. 1. Introduction. The compound Poisson insurance risk model perturbed by diffusion was first introduced by Gerber [8] and further studied by many authors, such as Dufresne and Gerber [7], Yuen et al. [23], Asmussen [1], Chiu and Yin [5], Lu et al. [15]. If investment income is introduced in the perturbed compound Poisson model, the security loading will be a variable. In the field of actuarial mathematics, researchers paid lots of attention to the issue of stochastic investment and debit, for example, Gerber [9], Zhu and Yang [24] considered the absolute ruin problem in the compound Poisson model when the debt and credit interest rates were the same. Cai [4] studied the Gerber – Shiu function in the classical insurance risk model with debit interest. Paulsen and Gjessing [19] simplified the version of the model which was used by Paulsen [16] through incorporating a stochastic rate of return on investments. Then they computed the probability of eventual ruin and the infinitesimal generator of the risk process. Gerber and Yang [11] proposed the general risk model with investment, in which the insurance company can invest its surplus in a risky asset and risk-free asset. If the company invests money in the bank or borrows money from the bank, the rate of return can be described as dRt = \left\{ rRtdt, if surplus is nonnegative, \alpha Rtdt, if surplus is negative, (1.1) where r is the company’s lending rate, \alpha is the borrowing rate which satisfies \alpha \geq r > 0. The model of the risky asset satisfies the stochastic differential equation * This research was supported by National Science Foundation of China (Grant No. 11571198); the Program for Shandong Postgradute Education Innovation Project (Grant No. SDYY16094). c\bigcirc Y. H. LU, Y. F. LI, 2019 ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 631 632 Y. H. LU, Y. F. LI dSt = \mu Stdt+ \sigma StdB0t, (1.2) where \mu t + \sigma B0t is the return on investment St to the risky asset, \{ B0t\} is the standard Brownian motion. Yin and Wen [22] extended the model of Paulsen [17] to the following form: Ut = u+ Pt + t\int 0 Us - dRs with P0 = R0 = 0, where \{ Pt\} , \{ Rt\} were independent Lévy processes, u was the initial value, \{ Pt\} was a general two-sided jump-diffusion risk model. Dividend strategies were first introduced by De Finetti [6]. He formulated the problem and solved it under the assumption that the surplus was a discrete process without investment. The study of the dividend strategy was also be conducted by Bühlmann [3], Paulsen [16], Jeanblanc-Picqué and Shiryaev [12], Asmussen and Taksar [2], Gerber and Shiu [10], Wan [20], Lu and Wu [14], Yin and Yuen [21]. Many results were obtained using the property of stationary and independent increments of the Poisson process and Brownian motion. Recently, Yin and Wen [22] extended the model raised by Paulsen [17] and obtained the integrodifferential equations of the Gerber – Shiu functions and total discounted dividends, respectively. For further references, see two survey papers Paulsen [17, 18]. In recent papers the model was extended to renewal risk model with stochastic return, see Yin and Wen [22] and Li [13]. Motivated by the previously mentioned papers, we are going to study the moment generating function of dividend value under barrier and threshold dividend strategies on a perturbed compound Poisson model with stochastic investment and debit interest. The rest of the paper is structured as follows. In Section 2, the perturbed compound Poisson model with stochastic investment and debit interest is introduced. In Section 3, the second-order integrodifferential equations for the moment generating function of aggregate dividends under the barrier dividend strategy are established. In the case of the exponential claim size, the exact solution of the third-order differential equations and the closed-form of the expected dividend value are obtained. In Section 4, the threshold dividend strategy is discussed. The integrodifferential equations for the moment generating function of aggregate dividends and the expected dividend value are obtained. 2. The insurance risk model with investment income. We consider a company with initial surplus u. If no dividends are paid, the surplus at time t is Pt = u+ ct - Nt\sum i=1 Xi + \sigma 1Wt, where c > 0 is the premium rate, \sigma 1 is a constant. The aggregate claim process \Bigl\{ \sum Nt i=1 Xi \Bigr\} is the compound Poisson process with parameter \lambda , \{ Xi\} is a sequence of independent and identically distributed random variables, the density function is defined as p(x). \{ Wt\} is the standard Brownian motion independent of the aggregate claim process. Now, suppose that the surplus is nonnegative, then the company can invest its money in a risk-free asset and a risky asset. The risk-free asset price is assumed to follow the stochastic differential equation (1.1), and the risky asset price is the same as (1.2). Wt and B0t are correlated with dWtdB0t = \rho dt. ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 DIVIDEND PAYMENTS IN A PERTURBED COMPOUND POISSON MODEL . . . 633 Assume that if the surplus Ut > 0 then the insurance company invests the surplus by a fixed proportion \tau to the risk-free asset and the rest proportion 1 - \tau of the surplus to the risky asset. If the surplus Ut \leq 0, then the insurance company borrows money from the bank under the debt rate \alpha . Hence, the modified surplus risk process \{ Ut\} satisfies the following equation. Let t > 0, for small enough \Delta t, \Delta Ut = Ut\Delta t\times \left\{ \tau r, Ut > 0, \alpha , Ut \leq 0, + (1 - \tau )Ut(\mu \Delta t+ \sigma \Delta B0t)\times \left\{ 1, Ut > 0, 0, Ut \leq 0, +\Delta Pt. Let initial u > 0, for small enough t and \Delta t = dt, we have dUs = \tau rUs - ds+ (1 - \tau )\mu Us - ds+ (1 - \tau )\sigma Us - dB0s + dPs = = [\tau r + (1 - \tau )\mu ]Us - ds+ (1 - \tau )\sigma Us - dB0s + dPs = = Us - dLs + dPs, 0 \leq s < t, (2.1) where Lt = adt+ bdB0t. We use a and b that are defined below a = \tau r + (1 - \tau )\mu , b = (1 - \tau )\sigma . From (2.5) in Yin and Wen [22] as a special case we get the another form of the equation (2.1) listed as follows: Ut = u+ t\int 0 (c+ aUs) ds+ t\int 0 \sqrt{} (\sigma 1 + \rho bUs - )2 + b2(1 - \rho 2)U2 s - dBs - Nt\sum i=1 Xi, u > 0, where \{ Bt, t \geq 0\} is a standard Brownian motion independent of the compound Poisson processes involved. If u \leq 0, for small enough t and \Delta t = dt, then \{ Ut\} satisfies the equation dUt = dPt + \alpha Utdt. (2.2) To solve the stochastic differential equation (2.2) we consider the process Vt = Ute - \alpha t. By using the product rule, we have dVt = e - \alpha tdUt - \alpha e - \alpha tUtdt. Combining with (2.2) we obtain dVt = e - \alpha tdPt. This gives Vt = V0 + \int t 0 e - \alpha sdPs. The solution for stochastic differential equation (2.2) is Ut = e\alpha t \left( u+ c t\int 0 e - \alpha sds \right) - e\alpha t t\int 0 e - \alpha sd Ns\sum i=1 Xi + \sigma 1e \alpha t t\int 0 e - \alpha sdW (s), u \leq 0. According to the above results, for small enough t > 0, we get the model Ut = \left\{ u+ \int t 0 (c+ aUs) ds+ \int t 0 \sqrt{} (\sigma 1 + \rho bUs - ) 2 + b2 (1 - \rho 2)U2 s - dBs - \sum Nt i=1 Xi, u > 0, e\alpha t \biggl( u+ c \int t 0 e - \alpha sds \biggr) - e\alpha t \int t 0 e - \alpha sd \sum Ns i=1 Xi + \sigma 1e \alpha t \int t 0 e - \alpha sdW (s), u \leq 0. (2.3) We assume that the company can still run as long as the surplus is above the level - c/\alpha , that is, if the surplus is below - c/\alpha , then the company’s interest can no longer pay off the debt and absolute ruin occurs immediately. ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 634 Y. H. LU, Y. F. LI 3. The barrier dividend strategy of the model. In this section we focus on the barrier dividend strategy. If the surplus Ut \geq \eta , \eta > 0, then the excess D(t) = Ut - \eta all will be paid to the shareholders as dividends. However, if the surplus Ut < \eta , then no dividends are paid. If the surplus is below - c \alpha , then absolute ruin happens and the surplus process stops. We define the dividend value until time t: Dt(\eta ) = t\int 0 I(Us > \eta )dD(s). Then the modified surplus is U\eta (t) = Ut - Dt(\eta ), where \{ Ut\} is modeled by (2.3). For simplicity, we let E[\cdot | U0 = u] = Eu(\cdot ). We denote V (u, \eta ) as the dividend value function of the strategy, which is V (u, \eta ) = Eu[DT1 ], where DT1 = \int T1 0 e - \delta tdDt(\eta ), \delta > 0 is the force of interest for valuation, and T1 is the absolute ruin time defined by T1 = \mathrm{i}\mathrm{n}\mathrm{f} \Bigl\{ t \geq 0, Ut(\eta ) \leq - c \alpha \Bigr\} . Let M(u, y, \eta ) = Eu[e yDT1 ] be the moment generating function of DT1 and M(u, y, \eta ) = \left\{ ey[(u - \eta )+V (\eta ,\eta )], u > \eta , M1(u, y, \eta ), 0 \leq u \leq \eta , M2(u, y, \eta ), - c \alpha < u < 0. We assume that, for any y < \infty , M(u, y, \eta ) exists, M1(u, y, \eta ) and M2(u, y, \eta ) are twice continu- ously differentiable for u \in \Bigl( - c \alpha , \eta \Bigr) . Theorem 3.1. If 0 < u < \eta , then M1(u, y, \eta ) satisfies the integrodifferential equation \lambda M1(u, y, \eta ) = (au+ c) \partial M1(u, y, \eta ) \partial u - \delta y \partial M1(u, y, \eta ) \partial y + + 1 2 (\sigma 2 1 + 2\rho b\sigma 1u+ b2u2) \partial 2M1(u, y, \eta ) \partial u2 + +\lambda u\int 0 M1(u - x, y, \eta )p(x) dx+ +\lambda u+ c \alpha \int u M2(u - x, y, \eta )p(x) dx+ \lambda \infty \int u+ c \alpha p(x) dx. (3.1) ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 DIVIDEND PAYMENTS IN A PERTURBED COMPOUND POISSON MODEL . . . 635 If - c \alpha < u < 0, then M2(u, y, \eta ) satisfies the following equation: \lambda M2(u, y, \eta ) = 1 2 \sigma 2 1 \partial 2M2(u, y, \eta ) \partial u2 + (\alpha u+ c) \partial M2(u, y, \eta ) \partial u - \delta y \partial M2(u, y, \eta ) \partial y + +\lambda u+ c \alpha \int 0 M2(u - x, y, \eta )p(x) dx+ \lambda \infty \int u+ c \alpha p(x) dx (3.2) with boundary conditions M2 \Bigl( - c \alpha , y, \eta \Bigr) = 1, M1(0+, y, \eta ) = M2(0 - , y, \eta ), \partial M(u, y, \eta ) \partial u \bigm| \bigm| \bigm| \bigm| u=\eta = yM1(\eta , y, \eta ). (3.3) Proof. If 0 \leq u < \eta , we consider an infinitesimal time interval (0, t). By the Markov property of the process \{ Ut\} , we have Mi(u, y, \eta ) = EuMi(Ut, ye - \delta t, \eta ) + o(t), i = 1, 2, 0 \leq u < \eta . (3.4) Let A d = B means that A and B have the same distribution. Set Yt = u+ t\int 0 (c+ aUs)ds+ t\int 0 \sqrt{} (\sigma 1 + \rho bUs - )2 + b2(1 - \rho 2)U2 s - dBs. In the infinitesimal time interval (0, t), the insurance risk process (2.3) has three possible cases. (i) If no jump happen in (0, t), then its probability is e\lambda t and Ut d = Yt. (ii) If there is only one jump in (0, t) and the claim size is X1, then its probability is \lambda te - \lambda t and Ut d = Yt - X1. Further, according to the amount of the claim, there are the following situations: (1) if 0 < X1 < Yt, then ruin do not occur, (2) if Yt < X1 < Yt + c \alpha , then the ruin occur, (3) if X1 \geq Yt + c \alpha , then the absolute ruin occur. (iii) If there are two or more jumps, then its probability is o(t). So, we have M1(u, y, \eta ) = e - \lambda tEu \bigl[ M1(Yt, ye - \delta t, \eta ) \bigr] + +\lambda te - \lambda tEu Yt\int 0 M1(Yt - x, ye - \delta t, \eta )p(x) dx+ +\lambda te - \lambda tEu Yt+ c \alpha \int Yt M2(Yt - x, ye - \delta t, \eta )p(x) dx+ ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 636 Y. H. LU, Y. F. LI +\lambda te - \lambda tEu \infty \int Yt+ c \alpha p(x) dx+ o(t). (3.5) By Itô’s formula, we obtain dM1(Yt, ye - \delta t, \eta ) = \partial M1(Yt, ye - \delta t, \eta ) \partial u dYt + y \partial M1(Yt, ye - \delta t, \eta ) \partial y de - \delta t+ + 1 2 \partial 2M1(Yt, ye - \delta t, \eta ) \partial u2 (dYt) 2. Then EuM1(Yt, ye - \delta t, \eta ) = M1(u, y, \eta )+ +Eu \left[ t\int 0 (c+ aUs) \partial M1(Ys, ye - \delta s, \eta ) \partial u ds - \delta y t\int 0 \partial M1(Ys, ye - \delta s, \eta ) \partial y e - \delta sds \right] + + 1 2 Eu t\int 0 \partial 2M1(Ys, ye - \delta s, \eta ) \partial u2 \bigl[ (\sigma 1 + \rho bUs - ) 2 + b2(1 - \rho 2)U2 s - \bigr] ds. (3.6) Substituting (3.6) into (3.5) and dividing both sides of (3.4) by t, then letting t \rightarrow 0 and rearranging it we get (3.1). If - c \alpha < u < 0, we let that h\alpha (t, u) = ue\alpha t + c(e\alpha t - 1) \alpha + \sigma 1e \alpha t t\int 0 e - \alpha s dWs. By full probability formula we have M2(u, y, \eta ) = e - \lambda tM2(h\alpha (t, u), ye - \delta t, \eta )+ +\lambda te - \lambda tEu h\alpha + c \alpha \int 0 M2(h\alpha (t, u) - x, ye - \delta t, \eta )p(x) dx+ +\lambda te - \lambda tEu \infty \int h\alpha + c \alpha p(x) dx+ o(t). (3.7) By using Itô’s formula, we obtain dM2(h\alpha (t, u), ye - \delta t, \eta ) = \partial M2(h\alpha (t, u), ye - \delta t, \eta ) \partial u dh\alpha (t, u)+ + \partial M2(h\alpha (t, u), ye - \delta t, \eta ) \partial u dye - \delta t + 1 2 \partial 2M2(h\alpha (t, u), ye - \delta t, \eta ) \partial u2 (dh\alpha ) 2. (3.8) ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 DIVIDEND PAYMENTS IN A PERTURBED COMPOUND POISSON MODEL . . . 637 By using (3.7) and (3.8), we get (3.2). Noting that if u = - c \alpha , then T1 = 0 and DT1 = 0. So we have M2 \Bigl( - c \alpha , y, \eta \Bigr) = E - c \alpha \bigl( eyDT1 \bigr) = 1, M1(0+, y, \eta ) = M2(0 - , y, \eta ), due to Mi(u, y, \eta ), i = 1, 2, are continuous at u = 0. By the definition of M(u, y, \eta ), we get \partial M(u, y, \eta \partial u | u=\eta = yM1(\eta , y, \eta ). The boundary condi- tions (3.3) are obtained. Theorem 3.1 is proved. Let M(u, y, \eta ) = 1 + yV (u, \eta ) + o(y), for small enough y, where V (u, \eta ) = Eu[DT1 ] = \left\{ V1(u, \eta ), 0 < u < \eta , V2(u, \eta ), - c \alpha < u < 0. (3.9) Substituting (3.9) into (3.1) and (3.2), comparing the coefficients of y, we get the following results. Theorem 3.2. If 0 < u < \eta , then Vi(u, \eta ), i = 1, 2, satisfy the equation (\lambda + \delta )V1(u, \eta ) = 1 2 \bigl( b2u2 + 2\rho b\sigma 1u+ \sigma 2 1 \bigr) V \prime \prime 1 (u, \eta ) + (au+ c)V \prime 1(u, \eta )+ +\lambda u\int 0 V1(u - x, \eta )p(x)dx+ \lambda u+ c \alpha \int u V2(u - x, \eta )p(x)dx. (3.10) If - c \alpha < u < 0, then V2(u, \eta ) satisfies the equation (\lambda + \delta )V2(u, \eta ) = 1 2 \sigma 2 1V \prime \prime 2 (u, \eta ) + (\alpha u+ c)V \prime 2(u, \eta )+ +\lambda u+ c \alpha \int 0 V2(u - x, \eta )p(x) dx (3.11) with boundary conditions V \prime 1(\eta ) = 1, V \prime 1(0+) = V \prime 2(0 - ), V1(0+) = V2(0 - ). (3.12) Example 3.1. Assume that the claim size has an exponential distribution with the density function p(x) = e - x. Applying the operator \biggl( d du + 1 \biggr) on (3.10) and (3.11), we get the following results. If 0 < u < \eta , then V1(u, \eta ) satisfies the equation 1 2 \bigl( b2u2 + 2\rho b\sigma 1u+ \sigma 2 1 \bigr) V \prime \prime \prime 1 (u, \eta )+ + \biggl[ 1 2 (b2u2 + 2\rho b\sigma 1u+ \sigma 2 1) + (a+ b2)u+ \rho b\sigma 1 + c \biggr] V \prime \prime 1 (u, \eta )+ +(au+ c+ a - \delta - \lambda )V \prime 1(u, \eta ) - \delta V1(u, \eta ) = 0. (3.13) ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 638 Y. H. LU, Y. F. LI If - c \alpha < u < 0, then V2(u, \eta ) satisfies the equation 1 2 \sigma 2 1V \prime \prime \prime 2 (u, \eta ) + \biggl( \alpha u+ c+ 1 2 \sigma 2 1 \biggr) V \prime \prime 2 (u, \eta ) + (\alpha u - \lambda - \delta + \alpha )V \prime 2(u, \eta ) - \delta V2(u, \eta ) = 0. (3.14) Letting \delta = b2 = 0, \lambda = a+ c, then (3.13) gives the equation 1 2 \sigma 2 1V \prime \prime \prime 1 (u, \eta ) + \biggl( au+ c+ 1 2 \sigma 2 1 \biggr) V \prime \prime 1 (u, \eta ) + auV \prime 1(u, \eta ) = 0. Using substitutions x = au, V \prime 1(u, \eta ) = e - ug(x); z = ax+ac - a\sigma 2 1 2 , g(x) = 2 a2\sigma 2 1 f(x); t = - z2 2 , f(z) = h(t), (3.13) yields th\prime \prime (t) + \biggl( 1 2 - 2 a3\sigma 2 1 t \biggr) h\prime (t) + ch(t) = 0. (3.15) For convenience, we let \sigma 2 1a 3 = 2, thus (3.15) changes into a confluent hypergeometric equation th\prime \prime (t) + \biggl( 1 2 - t \biggr) h\prime (t) + ch(t) = 0. The general solution to the above equation is a linear combination of two independent solutions h(t) = c5H \biggl( - c, 1 2 , t \biggr) + c6L \biggl( - c, 1 2 , t \biggr) , where H \biggl( - c, 1 2 , t \biggr) and L \biggl( - c, 1 2 , t \biggr) are the first and second kind of confluent hypergeometric functions respectively, c5 and c6 are constants. Transforming back to the original variables, we get the following solution: V \prime 1(u, \eta ) = 2c5 a2\sigma 2 1 e - uH \biggl( - c, 1 2 , - a2(au+ c - \sigma 2 1/2) 2 2 \biggr) + + 2c6 a2\sigma 2 1 e - uL \biggl( - c, 1 2 , - a2(au+ c - \sigma 2 1/2) 2 2 \biggr) . So V1(u, \eta ) = \int u 0 V \prime 1(x) dx+ V1(0+, \eta ). Next, we compute c5, c6. For (3.14), let \sigma 1 = 0, we have (\alpha u+ c)V \prime \prime 2 (u, \eta ) + (\alpha u+ c - \lambda - \delta + \alpha )V \prime 2(u, \eta ) - \delta V2(u, \eta ) = 0. (3.16) With change of variable y = - u - c \alpha , g(y) = V2(u, \eta ), (3.16) becomes yg\prime \prime (y) + \biggl( \alpha - \lambda - \delta \alpha - y \biggr) g\prime (y) + \delta \alpha g(y) = 0. This is an confluent hypergeometric equation. The general solution is ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 DIVIDEND PAYMENTS IN A PERTURBED COMPOUND POISSON MODEL . . . 639 g(y) = c7( - y) \lambda +\delta \alpha eyH \biggl( 1 + \delta \lambda , 1 + \lambda + \delta \alpha , - y \biggr) + c8e yL \biggl( 1 - \delta \lambda , 1 - \lambda + \delta \alpha , - y \biggr) . Transforming back to the original variable, we have V2(u, \eta ) = g \Bigl( - u - c \alpha \Bigr) = c7 \Bigl( u+ c \alpha \Bigr) \lambda +\delta \alpha e - u - c \alpha H \biggl( 1 + \delta \lambda , 1 + \lambda + \delta \alpha , u+ c \alpha \biggr) + +c8e - u - c \alpha L \biggl( 1 - \delta \lambda , 1 - \lambda + \delta \alpha , u+ c \alpha \biggr) . (3.17) As \mathrm{l}\mathrm{i}\mathrm{m} u\downarrow - c \alpha V2(u, \eta ) = c8L \biggl( 1 - \delta \lambda , 1 - \lambda + \delta \alpha , 0 \biggr) = c8 \Gamma \Bigl( \delta + \delta \alpha \Bigr) \Gamma \Bigl( 1 + \delta \alpha \Bigr) = 0, so c8 = 0. Letting \delta = 0 in (3.17), then we obtain V2(u, \eta ) = c7 \Bigl( u+ c \alpha \Bigr) \lambda \alpha e - u - c \alpha H \biggl( 1, 1 + \lambda \alpha , u+ c \alpha \biggr) . By using the boundary condition (3.12), we get 2c5 a2\sigma 2 1 e - \eta H \biggl( - c, 1 2 , - a2(a\eta - \sigma 2 1/2) 2 2 \biggr) + 2c6 a2\sigma 2 1 e - \eta L \biggl( - c, 1 2 , a2(a\eta + c+ \sigma 2 1/2) 2 \biggr) = 1, (3.18) V \prime 1(0+) = 2c5 a2\sigma 2 1 H \biggl( - c, 1 2 , - a2(c - \sigma 2 1/2) 2 2 \biggr) + 2c6 a2\sigma 2 1 L \biggl( - c, 1 2 , - a2(c - \sigma 2 1/2) 2 8 \biggr) = = c7 \Bigl( c \alpha \Bigr) \lambda \alpha e - c \alpha \biggl[ \lambda c H \biggl( 1, 1 + \lambda \alpha , c \alpha \biggr) - H \biggl( 1, 1 + \lambda \alpha , c \alpha \biggr) + \alpha \alpha + \lambda H \biggl( 2, 2 + \lambda \alpha , c \alpha \biggr) \biggr] = = V \prime 2(0 - ), (3.19) and V1(0+) = 2c5 a2\sigma 2 1 \eta \int 0 e - xH \biggl( - c, 1 2 , - a2(ax - \sigma 2 1/2) 2 2 \biggr) dx+ + 2c6 a2\sigma 2 1 \eta \int 0 e - xL \biggl( - c, 1 2 , a2(ax+ c+ \sigma 2 1/2) 2 \biggr) dx = = c7 \Bigl( c \alpha \Bigr) \lambda \alpha H \biggl( 1, 1 + \lambda \alpha ; c \alpha \biggr) = V2(0 - ). (3.20) Let P = \lambda c H \biggl( 1, 1 + \lambda \alpha , c \alpha \biggr) - H \biggl( 1, 1 + \lambda \alpha , c \alpha \biggr) + \alpha \alpha + \lambda H \biggl( 2, 2 + \lambda \alpha , c \alpha \biggr) , ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 640 Y. H. LU, Y. F. LI A1 = \eta \int 0 e - xH \biggl( - c, 1 2 , - a2(ax - \sigma 2 1/2) 2 2 \biggr) dx, B1 = \eta \int 0 e - xL \biggl( - c, 1 2 , a2(ax+ c+ \sigma 2 1/2) 2 \biggr) dx, A2 = H \biggl( - c, 1 2 , - a2(a\eta - \sigma 2 1/2) 2 2 \biggr) , B2 = L \biggl( - c, 1 2 , - a2(c - \sigma 2 1/2) 2 8 \biggr) , A3 = H \biggl( - c, 1 2 , - a2(c - \sigma 2 1/2) 2 2 \biggr) , B3 = L \biggl( - c, 1 2 , - a2(c - \sigma 2 1/2) 2 8 \biggr) , then (3.18), (3.19) and (3.20) can be rewritten by 2c5 a2\sigma 2 1 A2 + 2c6 a2\sigma 2 1 B2 = e\eta , 2c5 a2\sigma 2 1 A3 + 2c6 a2\sigma 2 1 B3 = c7 \Bigl( c \alpha \Bigr) \lambda \alpha e - c \alpha P, 2c5 a2\sigma 2 1 A1 + 2c6 a2\sigma 2 1 B1 = c7 \Bigl( c \alpha \Bigr) \lambda \alpha e - c \alpha H \biggl( 1, 1 + \lambda \alpha , c \alpha \biggr) . The solutions to the above three equations are c5 = a2\sigma 2 1e \eta 2 B1P - B3H \biggl( 1, 1 + \lambda \alpha , c \alpha \biggr) (A2B1 - A1B2)P +H \biggl( 1, 1 + \lambda \alpha , c \alpha \biggr) (B2A3 - A2B3) , c6 = a2\sigma 2 1e \eta 2 A3H \biggl( 1, 1 + \lambda \alpha , c \alpha \biggr) - A1P (A2B1 - A1B2)P +H \biggl( 1, 1 + \lambda \alpha , c \alpha \biggr) (B2A3 - A2B3) , c7 = e c \alpha +\eta \Bigl( \alpha c \Bigr) \lambda \alpha P (B1A3 - A1B3) (A2B1 - A1B2)P +H \biggl( 1, 1 + \lambda \alpha , c \alpha \biggr) (B2A3 - A2B3) . 4. The threshold dividend strategy. In this section, we consider the threshold dividend strategy for surplus Ut, where Ut is defined by (2.3). The company will pay dividends to its shareholders according to the following strategy governed by parameters \eta > 0 and \beta > 0. Whenever the (modified) surplus is below the level \eta , no dividends are paid. However, when the modified surplus ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 DIVIDEND PAYMENTS IN A PERTURBED COMPOUND POISSON MODEL . . . 641 is above \eta , dividends are paid continuously at a constant rate \beta . If the surplus is below the level - c \alpha , the absolute ruin happens and the dividend process stops. Let \~Dt(\eta ) denote the aggregate dividends paid by time t \geq 0. The modified surplus process \~U\eta (t) is given by \~U\eta (t) = Ut - \~Dt(\eta ). Let \delta > 0 be the force of interest for valuation, and let DT2 denote the present value of all dividends until the absolute ruin, DT2 = T2\int 0 e - \delta td \~Dt(\eta ), where T2 = \mathrm{i}\mathrm{n}\mathrm{f} \Bigl\{ t > 0, \~Ut(\eta ) \leq - c \alpha \Bigr\} . We denote \~V (u, \eta ) as the expected dividend value function of the strategy, that is \~V (u, \eta ) = Eu[DT2 ]. Let \~M(u, y, \eta ) = Eu[e yDT2 ] be the moment generating function of DT2 . For any y < \infty , we have 0 < \~M(u, y, \eta ) \leq \mathrm{l}\mathrm{i}\mathrm{m}u\uparrow \infty \~M(u, y, \eta ) = ey \beta \delta < +\infty , then \~M(u, y, \eta ) exists. We define \~M(u, y, \eta ) = \left\{ \~M1(u, y, \eta ), if u \geq 0, \~M2(u, y, \eta ), if - c \alpha < u < 0. Theorem 4.1. Suppose that \~M(u, y, \eta ) is twice continuously differentiable u \in \Bigl( - c \alpha , \eta \Bigr) , then \~M1(u, y, \eta ) and \~M2(u, y, \eta ) satisfy the following equations: \lambda \~M2(u, y, \eta ) = (\alpha u+ c) \partial \~M2(u, y, \eta ) \partial u - \delta y \partial \~M2(u, y, \eta ) \partial y + 1 2 \sigma 2 1 \partial 2 \~M2(u, y, \eta ) \partial u2 + +\lambda u+ c \alpha \int 0 \~M2(u - x, y, \eta )p(x) dx+ \lambda \infty \int u+ c \alpha p(x) dx, - c \alpha < u < 0, (4.1) \lambda \~M1(u, y, \eta ) = (au+ c) \partial \~M1(u, y, \eta ) \partial u - \delta y \partial \~M1(u, y, \eta ) \partial y + + 1 2 (b2u2 + 2\rho b\sigma 1u+ \sigma 2 1) \partial 2 \~M1(u, y, \eta ) \partial u2 + \lambda u\int 0 \~M1(u - x, y, \eta )p(x) dx+ +\lambda u+ c \alpha \int u \~M2(u - x, y, \eta )p(x) dx+ \lambda \infty \int u+ c \alpha p(x) dx, 0 \leq u < \eta , (4.2) (\lambda - y\beta ) \~M1(u, y, \eta ) = 1 2 (b2u2 + 2\rho b\sigma 1u+ \sigma 2 1) \partial 2 \~M1(u, y, \eta ) \partial u2 + ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 642 Y. H. LU, Y. F. LI + \bigl[ (c - \beta ) + au - \delta y \bigr] \partial \~M1(u, y, \eta ) \partial y + \lambda u\int 0 \~M1(u - x, y, \eta )p(x) dx+ +\lambda u+ c \alpha \int u \~M2(u - x, y, \eta )p(x) dx+ \lambda \infty \int u+ c \alpha p(x) dx, u \geq \eta , (4.3) with boundary conditions \~M2 \Bigl( - c \alpha , y, \eta \Bigr) = 1, \mathrm{l}\mathrm{i}\mathrm{m} u\uparrow \infty \~M1(u, y, \eta ) = ey \beta \delta , \~M1(0+, y, \eta ) = \~M2(0 - , y, \eta ). Proof. The proof of (4.1), (4.2) are similar to (3.1), (3.2), and are omitted. Next, we prove (4.3). By Markovian property, we get \~M(u, y, \eta ) = Eu[ \~M(Ut, ye - \delta t, \eta )] + o(t). Hence, \~M1(u, y, \eta ) = (1 - \lambda t)e - \lambda tey\beta tEu[ \~M1(u, ye - \delta t, \eta )]+ +\lambda te - \lambda tey\beta tEu Zt\int 0 \~M1(Zt - x, ye - \delta t, \eta )p(x) dx+ +\lambda te - \lambda tey\beta tEu Zt+ c \alpha \int Zt \~M2(Zt - x, ye - \delta t, \eta )p(x) dx+ +\lambda te - \lambda tey\beta tEu \infty \int Zt+ c \alpha p(x) dx+ o(t), where Zt = u+ t\int 0 (c - \beta + aUs)ds+ t\int 0 \sqrt{} (\sigma 1 + \rho bUs - )2 + b2(1 - \rho 2)U2 s - dBs. By using the same arguments as in the proof of Theorem 3.1, we get (4.3). Noting that if u = - c \alpha , then T2 = 0 and DT2 = 0. So we have \~M2 \Bigl( - c \alpha , y, \eta \Bigr) = E - c \alpha \bigl( eyDT2 \bigr) = 1. \~M1(0+, y, \eta ) = \~M2(0 - , y, \eta ) due to \~M(u, y, \eta ) is continuous at u = 0. By the definition of \~M1(u, y, \eta ), we get \mathrm{l}\mathrm{i}\mathrm{m}u\uparrow \infty \~M1(u, y, \eta ) = ey \beta \delta . The boundary conditions for \~Mi, i = 1, 2, are obtained. Theorem 4.1 is proved. Set \~M(u, y, \eta ) = 1 + y \~V (u, \eta ) + o(y), where ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 DIVIDEND PAYMENTS IN A PERTURBED COMPOUND POISSON MODEL . . . 643 \~V (u, \eta ) = Eu[DT2 ] = \left\{ \~V1(u, \eta ), u \geq 0, \~V2(u, \eta ), - c \alpha < u < 0. (4.4) Substituting (4.4) into (4.1), (4.2) and (4.3), comparing the coefficients of y, we get the following results. Theorem 4.2. If - c \alpha < u < 0, then \~V2(u, \eta ) in (4.4) satisfies the equation (\delta + \lambda ) \~V2(u, \eta ) = (\alpha u+ c) \~V \prime 2(u, \eta ) + 1 2 \sigma 2 1 \~V \prime \prime 2 (u, \eta )+ +\lambda u+ c \alpha \int 0 \~V2(u - x, y, \eta )p(x) dx+ \lambda \infty \int u+ c \alpha p(x) dx. (4.5) If 0 \leq u < \eta , then \~Vi(u, \eta ), i = 1, 2, in (4.4) satisfy the equation (\delta + \lambda ) \~V1(u, \eta ) = (au+ c) \~V \prime 1(u, \eta ) + 1 2 (b2u2 + 2\rho b\sigma 1u+ \sigma 2 1) \~V \prime \prime 1 (u, \eta )+ +\lambda u\int 0 \~V1(u - x, \eta )p(x) dx+ \lambda u+ c \alpha \int u \~V2(u - x, \eta )p(x) dx+ \lambda \infty \int u+ c \alpha p(x) dx. (4.6) If u \geq \eta , then \~Vi(u, \eta ), i = 1, 2, in (4.4) satisfy the equation (\delta + \lambda ) \~V1(u, \eta ) = 1 2 (b2u2 + 2\rho b\sigma 1u+ \sigma 2 1) \~V \prime \prime 1 (u, \eta ) + (c - \beta + au) \~V \prime 1(u, \eta )+ +\lambda u\int 0 \~V1(u - x, \eta )p(x) dx+ \lambda u+ c \alpha \int u \~V2(u - x, \eta )p(x) dx+ \beta (4.7) with boundary conditions \~V2 \Bigl( - c \alpha +, \eta \Bigr) = 0, \mathrm{l}\mathrm{i}\mathrm{m} u\uparrow \infty \~V1(u, \eta ) = \beta \delta , \~V1(0+, \eta ) = \~V2(0 - , \eta ), \~V \prime 1(0+, \eta ) = \~V \prime 2(0 - , \eta ), \~V \prime 1(\eta +, \eta ) = \~V \prime 1(\eta - , \eta ), \~V1(\eta +, \eta ) = \~V1(\eta - , \eta ). Remark 4.1. Letting \lambda = 0 in (4.5), (4.6) and (4.7), then they can be changed to \delta \~V2(u, \eta ) = (\alpha u+ c) \~V \prime 2(u, \eta ) + 1 2 \sigma 2 1 \~V \prime \prime 2 (u, \eta ), - c \alpha < u < 0, (4.8) \delta \~V1(u, \eta ) = (au+ c) \~V \prime 1(u, \eta ) + 1 2 (b2u2 + 2\rho b\sigma 1u+ \sigma 2 1) \~V \prime \prime 1 (u, \eta ), 0 \leq u < \eta , (4.9) \delta \~V (u, \eta ) = 1 2 (b2u2 + 2\rho b\sigma 1u+ \sigma 2 1) \~V \prime \prime 1 (u, \eta ) + (c - \beta + au) \~V \prime (u, \eta ) + \beta , u \geq \eta . (4.10) In the case of u \geq 0, (4.9) and (4.10) are obtained by Yin and Wen [22], where they got the same results by using different methods. We extend their results for the more general case. ISSN 1027-3190. Укр. мат. журн., 2019, т. 71, № 5 644 Y. H. LU, Y. F. LI References 1. Asmussen S. Ruin probabilities. – Singapore: World Sci., 2000. 2. Asmussen S., Taksar M. 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spelling umjimathkievua-article-14622019-12-05T08:56:08Z Dividend payments in a perturbed compound Poisson model with stochastic investment and debit interest Дивiденднi виплати у збуренiй складнiй пуассонiвськiй моделi зi стохастичними iнвестицiями та дебетовими вiдсотками Li, Y. F. Lu, Y. H. Лі, Я. Ф. Лю, Я. Х. UDC 519.21 We consider a compound Poisson insurance risk model perturbed by diffusion with stochastic return on investment and debit interest. If the initial surplus is nonnegative, then the insurance company can invest its surplus in a risky asset and risk-free asset based on a fixed proportion. Otherwise, the insurance company can get the business loan when the surplus is negative. The integrodifferential equations for the moment generating function of the cumulative dividends value are obtained under the barrier and threshold dividend strategies, respectively. The closed-form of the expected dividend value is obtained when the claim amount is exponentially distributed. УДК 519.21 Розглядається складна пуассонівська модель страхових ризиків, збурена дифузією, зі стохастичним доходом по інвестиціях та дебетовим відсотком. Якщо початковий надлишок є невід&#039;ємним, то стрaхова компанія може вкладати цей надлишок у ризикові або безризикові активи в фіксованій пропорції. В протилежному випадку, коли надлишок є від&#039;ємним, страхова компанія може отримувати бізнесові кредити. Інтегро-диференціальні рівняння для функції, що породжує моменти значень кумулятивних дивідендів, отримано для бар&#039;єрних та порогових дивідендних стратегій відповідно. Очікувану величину дивідендів отримано в замкненій формі у випадку експоненціального розподілу суми позову. Institute of Mathematics, NAS of Ukraine 2019-05-25 Article Article application/pdf https://umj.imath.kiev.ua/index.php/umj/article/view/1462 Ukrains’kyi Matematychnyi Zhurnal; Vol. 71 No. 5 (2019); 631-644 Український математичний журнал; Том 71 № 5 (2019); 631-644 1027-3190 en https://umj.imath.kiev.ua/index.php/umj/article/view/1462/446 Copyright (c) 2019 Li Y. F.; Lu Y. H.
spellingShingle Li, Y. F.
Lu, Y. H.
Лі, Я. Ф.
Лю, Я. Х.
Dividend payments in a perturbed compound Poisson model with stochastic investment and debit interest
title Dividend payments in a perturbed compound Poisson model with stochastic investment and debit interest
title_alt Дивiденднi виплати у збуренiй складнiй пуассонiвськiй моделi зi стохастичними iнвестицiями та дебетовими вiдсотками
title_full Dividend payments in a perturbed compound Poisson model with stochastic investment and debit interest
title_fullStr Dividend payments in a perturbed compound Poisson model with stochastic investment and debit interest
title_full_unstemmed Dividend payments in a perturbed compound Poisson model with stochastic investment and debit interest
title_short Dividend payments in a perturbed compound Poisson model with stochastic investment and debit interest
title_sort dividend payments in a perturbed compound poisson model with stochastic investment and debit interest
url https://umj.imath.kiev.ua/index.php/umj/article/view/1462
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