±¨¸æÌâÄ¿1£ºA frequency domain for the stabilizing feedback controller of linear delay systems
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±¨¸æÕªÒª£ºWe investigate feedback stabilization of linear delay systems. When the unstable characteristic roots of the system are far from the imaginary axis, the discretization of unstable differential equations results in a large error. In this case, it is difficult to seek stabilizing control laws via the algorithm in the literature. In order to avoid the discretization of unstable differential equations, a modified state equation is constructed through a shifting parameter such that the equation is asymptotically stable. Then, based on the modified state equation and Parseval¡¯s theorem, a numerical optimization algorithm is provided to design a stabilizing controller. Meanwhile, we compare the presented algorithm with that in the literature. Finally, numerical examples are given to illustrate the presented algorithm.
±¨¸æÌâÄ¿2£ºCompensated split-step balanced methods for nonlinear stiff SDEs with jump-diffusion and piecewise continuous arguments
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±¨¸æÊ±¼ä£º2022Äê11ÔÂ26ÈÕ 14:00
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±¨¸æÈ˼ò½é£ºÕųϼá, »ªÖпƼ¼´óѧ¶þ¼¶½ÌÊÚ, ²©Ê¿Éúµ¼Ê¦. 1998Äê±ÏÒµÓÚºþÄÏ´óѧӦÓÃÊýѧרҵ»ñÀíѧ²©Ê¿Ñ§Î»ºó, µ÷È뻪ÖÐÀí¹¤´óѧÊýѧϵ£¬²¢Í¬Ê±½øÈë¸ÃУ¿ØÖÆ¿ÆÑ§Ó빤³Ì²©Ê¿ºóÁ÷¶¯Õ¾¹¤×÷(2000Äê³öÕ¾). 2002Äê2ÔÂÖÁ2004Äê3ÔÂÔÚ±ÈÀûʱ³ãë´óѧ¼ÆËã»ú¿ÆÑ§Ïµ×öºÏ×÷Ñо¿¹¤×÷.Ôøµ£ÈλªÖпƼ¼´óѧÊýѧÓëͳ¼ÆÑ§ÔºÔº³¤¡¢ÖйúÊýѧѧ»áµÚÊ®½ì¡¢Ê®Ò»½ìÀíÊ¡¢Öйú¼ÆËãÊýѧѧ»áµÚÆß½ì¡¢°Ë½ì³£ÎñÀíʼ°ºþ±±Ê¡Êýѧѧ»á¸±Àíʳ¤. ÏÖ¼æÈÎÖйú·ÂÕæË㷨רҵίԱ»á¸±Ö÷ÈÎίԱ¡¢ÖйúÊýѧѧ»áÆæÒìÉ㶯רҵίԱ»áίԱ¡¢ºþ±±Ê¡¹¤³Ì½¨Ä£Óë¿ÆÑ§¼ÆËãÖØµãʵÑéÊÒÖ÷ÈΡ¢¡¶Applied Mathematics and Computation¡·¸±Ö÷±à¼°¡¶Mathematics and Computers in Simulation¡·¡¢¡¶Acta Mathematica Scientia¡·µÈ¹ú¼ÊѧÊõÆÚ¿¯±àί.Ö÷Òª´ÓʸÕÐÔʱœþ΢·Ö·½³ÌÊýÖµ½â¼°ÆäËã·¨ÀíÂÛÑо¿£¬Ö÷³ÖÓйú¼Ò×ÔÈ»¿ÆÑ§»ù½ðÃæÉÏÏîÄ¿6Ïî¡¢½ÌÓý²¿Áôѧ»Ø¹úÈËÔ±Æô¶¯»ù½ð¼°ºþ±±Ê¡×ÔÈ»¿ÆÑ§»ù½ð¸÷1Ï²¢×÷ΪÖ÷Òª³ÉÔ±³Ðµ£¹ý¹ú¼Ò×ÔÈ»¿ÆÑ§»ù½ðÖØ´óÑо¿¼Æ»®¿ÎÌâºÍ¹ú¼Ò¸ß¼¼ÊõÑо¿·¢Õ¹¼Æ»®ÖصãÏîÄ¿. ÔÚ¡¶SIAM J. Sci. Comput.¡·¡¢¡¶IMA J. Numer. Anal. ¡·¡¢¡¶Numer. Math.¡·µÈ¹úÄÚÍâѧÊõÆÚ¿¯·¢±íSCIÊÕ¼ÂÛÎÄ100ÓàÆª£¬Ö÷¡¢²Î±à½Ì²Ä5²¿£¬Ö÷³ÖÓйú¼Ò¼¶¾«Æ·¿Î³Ì¼°¹ú¼Ò¼¶¾«Æ·×ÊÔ´¹²Ïí¿Î¡¶¼ÆËã·½·¨¡·. Ôø»ñ¹úÎñÔºÕþ¸®ÌØÊâ½òÌù¡¢»úе¹¤Òµ²¿¿Æ¼¼½ø²½¶þµÈ½±¡¢ºþ±±Ê¡×ÔÈ»¿ÆÑ§½±¶þµÈ½±¡¢ºþ±±Ê¡ÓÐÍ»³ö¹±Ï×µÄÖÐÇàÄêר¼Ò¡¢±¦¸ÖÓÅÐã½Ìʦ½±¡¢ºþ±±Ê¡ÓÅÐã½Ìѧ³É¹ûÒ»µÈ½±¼°ºþ±±Ê¡ÓÅÐã½ÌÓý¹¤×÷ÕßµÈ.
±¨¸æÕªÒª£ºThis talk is concerned with numerical solutions of nonlinear stiff stochastic differential equations with jump-diffusion and piecewise continuous arguments. By combining compensated split-step methods and balanced methods, a class of compensated split-step balanced (CSSB) methods are suggested for solving the equations. Based on the one-sided Lipschitz condition and local Lipschitz condition, a strong convergence criterion of CSSB methods is derived. It is proved under some suitable conditions that the numerical solutions produced by CSSB methods can preserve the mean-square exponential stability of the corresponding analytical solutions. Several numerical examples are presented to illustrate the obtained theoretical results and the effectiveness of CSSB methods. Moreover, in order to show the computational advantage of CSSB methods, we also give a numerical comparison with the adapted split-step backward Euler methods with or without compensation and tamed explicit methods.
±¨¸æÌâÄ¿3£ºNumerical analysis of a time discretized method for nonlinear filtering problem with diffusive and point process observations
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±¨¸æÕªÒª£ºIn this paper we consider a nonlinear filter model with observations driven by correlated diffusive processes and point process. We first derive a Zakai equation whose solution is an unnormalized probability density function of the filter solution. Then we apply a splitting-up technique to decompose the Zakai equation into three regular easily solvable stochastic differential equations, based on which we construct a splitting-up approximate solution and derive its convergence of first order. Furthermore, we use difference method to construct a semi-discretized approximate solution of Zakai equation and prove the convergence is of half order. Finally we present some numerical experiments to demonstrate the theoretical analysis.
±¨¸æÌâÄ¿4£ºPositivity preserving logarithmic Euler-Maruyama type scheme for stochastic differential equations
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±¨¸æÕªÒª£ºA logarithmic truncated Euler-Maruyama method is proposed to preserve the positivity of the general stochastic differential equations. The exponential integrability is proved for both the exact solution and the numerical solution. Moreover, under some reasonable conditions, the strong convergence rate of the underlying numerical method is obtained.
±¨¸æÌâÄ¿5£ºNumerical methods for weakly singular stochastic Volterra integral equations
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±¨¸æÕªÒª£ºIn this talk we first establish the existence, uniqueness and Holder continuity of the solution to stochastic Volterra integral equations (SVIEs) with weakly singular kernels, with singularities ¦Á ¡Ê (0, 1) for the drift term and ¦Â ¡Ê (0, 1/2) for the stochastic term. Subsequently, we propose a ¦È-Euler¨CMaruyama scheme and a Milstein scheme to solve the equations numerically and obtain strong rates of convergence for both schemes in Lp norm for any p ¡Ý1. For the Theta-Euler¨CMaruyama scheme the rate is min{1?¦Á, 1/2?¦Â} and for the Milstein scheme is min{1?¦Á, 1?2¦Â}. These results on the rates of convergence are significantly different from those it is similar schemes for the SVIEs with regular kernels. This talk is based on the joint work with Dr. Min Li and Professor Yaozhong Hu.
±¨¸æÌâÄ¿6£ºSingular stochastic Volterra integral equations: Well-posedness and numerical approximation
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±¨¸æÊ±¼ä£º2022Äê11ÔÂ26ÈÕ 16:00
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±¨¸æÕªÒª£ºThis talk focus on three classes of stochastic Volterra integral equations with weakly singular kernels from the perspective of well-posedness and numerical approximation.
1) For the stochastic fractional integro-differential equation with weakly singular kernels, it can be rewritten as an equivalent stochastic Volterra integral equation. We prove the well-posedness of the exact solution, the strong convergence of Euler-Maruyama (EM) approximation under local Lipschitz continuous and linear growth condition, and the strong convergence rate of EM approximation under global Lipschitz continuous and linear growth condition.
2) For L¨¦vy-driven stochastic Volterra integral equations with doubly singular kernels, we prove the well-posedness of the exact solution under local Lipschitz continuous and linear growth condition, and propose a fast EM method based on the sum-of-exponentials approximation, which improves the computational cost and efficiency of EM methods.
3) For the overdamped generalized Langevin equation with fractional noise, we extend the existing convergence result of the Euler method to general parameter cases by delicately treating the singular stochastic integral with respect to fractional Brownian motion.
±¨¸æÌâÄ¿7£ºStrong and weak convergence rates of logarithmic transformed truncated EM methods for SDEs with positive
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±¨¸æÕªÒª£ºTo inherit numerically the positivity of stochastic differential equations (SDEs) with non-globally Lipschitz coefficients, we devise a novel explicit method, called logarithmic transformed truncated Euler-Maruyama method. There is however a price to be paid for the preserving positivity, namely that the logarithmic transformation would cause the coefficients of the transformed SDEs growing super-linearly or even exponentially, which makes the strong and weak convergence analysis more complicated. Based on the exponential integrability, truncation techniques and some other arguments, we show that the strong convergence rate of the underlying numerical method is 1/2, and the weak convergence rate can be arbitrarily close to 1. To the best of our knowledge, this is the first result establishing the weak convergence rate of numerical methods for the general SDEs with positive solutions. Numerical experiments are finally reported to confirm our theoretical results.
±¨¸æÌâÄ¿8£ºCentral limit theorems for approximating ergodic limit of SPDEs via a full discretization
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±¨¸æÕªÒª£ºIn this talk, we focus on characterizing quantitatively the fluctuations between the ergodic limit and the time-averaging estimator of the full discretization for the parabolic stochastic partial differential equation. We establish a central limit theorem, which shows that the normalized time-averaging estimator converges to a normal distribution with the variance being the same as that of the continuous case, where the scale used for the normalization corresponds to the temporal strong convergence rate of the considered full discretization.
±¨¸æÌâÄ¿9£ºRegime-switching diffusion processes with infinite delay
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±¨¸æÕªÒª£ºIn this work we consider a class of regime-switching diffusion processes, which are determined by solutions X(t) to stochastic functional differential equation with infinite delay and random switching represented by jump process \Lambda(t). We first establish the existence and uniqueness of the underlying process by an interlacing procedure. Under suitable conditions, we then investigate convergence and boundedness of both the solution X(t) and the solution map X_{t}. We show that two solutions (resp. solution maps) from different initial data living in the same initial switching regime will be close with high probability as time variable tends to infinity, and that the solution (resp. solution map) is uniformly bounded in the mean square sense. Moreover, we prove existence and uniqueness of the invariant probability measure of two-component Markov-Feller process (X_{t}, \Lambda(t)), and establish exponential bounds on the rate of convergence to the invariant probability measure under Wasserstein distance. Finally, we provide a concrete example to illustrate our main results.
±¨¸æÌâÄ¿10£ºErgodicity and stability of hybrid systems with threshold type state-dependent switching
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±¨¸æÕªÒª£ºTo deal with stochastic hybrid systems with general state-dependent switching, we propose an approximation method by a sequence of stochastic hybrid systems with threshold type switching. The convergence rate in the Wasserstein distance is estimated in terms of the difference between transition rate matrices. Our method is based on an elaborate construction of coupling processes in terms of Skorokhod's representation theorem for jumping processes. Moreover, we establish explicit criteria on the ergodicity and stability for stochastic hybrid systems with threshold type switching. Some examples are given to illustrate the sharpness of these criteria.
±¨¸æÌâÄ¿11£ºUniform Poincare inequalities and logarithmic Sobolev inequalities for mean field particle systems
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±¨¸æÕªÒª£ºIn this talk we show some explicit and sharp estimates of the spectral gap and the log-Sobolev constant for mean field particles system, uniform in the number of particles, when the confinement potential have many local minimums. Our uniform log-Sobolev inequality, based on Zegarlinski¡®s theorem for Gibbs measures, allows us to obtain the exponential convergence in entropy of the McKean-Vlasov equation with an explicit rate constant, generalizing the result of Carrillo-McCann-Villani(2003) by means of the displacement convexity approach, or Malrieu(2001,2003) by Bakry-Emery technique or the recent work of Bolley-Gentil-Guillin by dissipation of the Wasserstein distance.This talk is based on a joint work with Arnaud Guillin, Liming Wu and Chaoen Zhang.
±¨¸æÌâÄ¿12£ºA probability approximation framework and its applications
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±¨¸æÕªÒª£ºBy embedding the classical Lindeberg principle into a Markov process and using conditional expectation, we establish a general probability approximation framework. As applications, we study the error bounds of the following three approximations: approximating online stochastic gradient descents (SGDs) by stochastic differential equations (SDEs), approximating stochastic variance reduced gradients (SVRGs) by stochastic differential delay equations (SDDEs), and the approximation of ergodic measure of stable SDEs by Euler-Maruyama scheme. More applications will be discussed. This talk is based on the joint works with P. Chen, J. Lu, X. Jin, and Q. M. Shao.
±¨¸æÌâÄ¿13£ºThe convergence rate of the equilibrium measure for the LQG mean field game with a common noise
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±¨¸æÈ˼ò½é£ºQingshuo Song's research interests include stochastic control theory and its applications to mathematical finance and various engineering problems. Qingshuo received his BSc from Nankai University and his Ph.D. from Wayne State University. Prior to joining Worcester Polytechnic Institute, he worked with the City University of Hong Kong (Associate Professor 2010-2018), the University of Michigan (PostDoc 2009), and the University of Southern California (PostDoc 2006-2009). He is currently an associate professor and doctoral supervisor at Worcester Polytechnic Institute, USA.
±¨¸æÕªÒª£ºThe convergence rate of equilibrium measures of N-player Games with Brownian common noise to its asymptotic Mean Field Game system is known as 1/9 with respect to 1-Wasserstein distance, obtained by the monograph [6, Cardaliaguet, Delarue, Lasry, Lions (2019)]. In this work, we study the convergence rate of the N-player LQG game with a Markov chain common noise towards its asymptotic Mean Field Game. The approach relies on an explicit coupling of the optimal trajectory of the N-player game driven by N-dimensional Brownian motion and the Mean Field Game counterpart driven by one-dimensional Brownian motion. As a result, the convergence rate is 1/2 with respect to the 2-Wasserstein distance. It's joint work with Jiamin Jian, Peiyao Lai, and Jiaxuan Ye.
±¨¸æÌâÄ¿14£ºMean square stability of stochastic theta method for stochastic differential equations driven by fractional Brownian motion
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±¨¸æÊ±¼ä£º2022Äê11ÔÂ26ÈÕ 21:00
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±¨¸æÈ˼ò½é£ºYaozhong Hu obtained his Ph.D in 1992 from Strasbourg University under the supervision of Paul Andre Meyer. He made significant contributions to stochastic analysis, fractional Brownian motions, stochastic partial differential equations and Malliavin calculus. He is currently a centennial professor and doctoral supervisor at University of Alberta at Edmonton, Canada.
±¨¸æÕªÒª£ºI will present a result on the mean square stability of the solution and its stochastic theta scheme for the linear stochastic differential equations driven by fractional Brownian motion with Hurst parameter 1/2<H<1.
±¨¸æÌâÄ¿15£ºPositivity and boundedness preserving numerical scheme for the stochastic epidemic model
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This work concerns about the numerical solution to the stochastic epidemic model proposed by Cai et al. in 2019. The typical features of the model including the positivity and boundedness of the solution and the presence of the square-root diffusion term make this an interesting and challenging work. By modifying the classical Euler-Maruyama (EM) scheme, we generate a positivity and boundedness preserving numerical scheme, which is proved to have a strong convergence to the true solution over finite time intervals. We also demonstrate that the principle of this method is applicable to a bunch of popular stochastic differential equation (SDE) models, e.g. the mean-reverting square-root process, an important financial model, and the multi-dimensional SDE SIR epidemic model. This is a joint work with Y. Cai and J. Hu.