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快速随机波动率变换下的信用风险定价研究
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摘要
本文在快速随机波动率变换的情况下研究了单个信用衍生品定价的风险规避问题。本文首先在Merton最优化的问题中添加随机波动率,将其应用到信用风险的研究中。假设波动率过程是一种不同时间尺度的扰动过程,对其进行近似估计。由于价值过程可看成是一个不完全市场围绕着完全市场常数波动率的一种扰动,故这种近似方法是可行的。其次,当波动率变换是快速均值回归过程时,这种扰动过程是一种关于Hamilton-Jacobi-Bellman偏微分方程的奇异扰动过程。当波动率变换非常缓慢时,这种扰动过程是一般的扰动过程。两种扰动过程叠加在一起便是多元时间维度随机波动率过程。再者,本文提出的算法与线性期权定价问题具有较高的一致性,因而也发现了风险容忍度方程的一些新性质。本文最后还在快速时间维度的框架下研究了波动率对于信用风险的投资优化问题。由于新建模型是一个非线性PDE,故不能直接给出其解析解,于是本文引进一种扰动逼近的方法,该方法的关键中间步骤是把问题分成可解和扰动两个部分。通过扰动逼近的方法,可得一个近似的解析解。
In this paper,we study the risk aversion on valuing the single-name credit derivatives by introducing the fast —scale stochastic volatility correction.Firstly,the paper studies the Merton portfolio problem in the presence of stochastic volatility,and applies it to the credit risk problem.We assume the volatility process is a perturbation process with various time scale,and estimate it approximately.This approach is feasible,because we treat the value function as a perturbation problem in the incomplete market,which is moving around the constant volatility of the complete market.Secondly,if the volatility is fast mean—reverting,it is a singular perturbation defined by a nonlinear Hamilton—Jacobi-Bellman PDE;If it is slowly varying,it is a regular perturbation problem.In this paper,we add the two processes together,which is a multiscale stochastic volatility problem.Thirdly,the algorithm shares remarkable similarities with the linear option pricing problem,but it gives new properties to the risk tolerance function.Finely,this paper is to study how fast — scale volatility affect the portfolio optimizing problem with single name credit risk under the frame of the fast scale stochastic volatility.Due to our model is a non—linear PDE,analytical solution cannot be obtained directly.In order to get the closed form solution,we introduce a method called perturbation approximation.A critical feature of the technique is that we break the problem into two solvable and perturbation parts.By using the perturbation approximation method,the approximated analytical solution can be obtained.
引文
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