提出可灵活控制右尾轻重的新型偏态分布,提升对复杂数据的建模能力。
Stochastic Processes with Modified Lognormal Distribution Featuring Flexible Upper Tail
- 基于广义kappa函数构造新分布,通过参数kappa调节右尾衰减速率。
- 推导出分布的矩与负对数似然梯度的解析表达式,支持高效参数估计。
- 适用于时间序列预测与空间插值,适合处理工程与自然科学中的偏斜数据。
非对称、非高斯概率分布常见于自然与工程数据中。对数正态分布是描述偏态频数直方图和厚尾数据的标准模型,但其在高值处对概率密度与风险函数的渐近依赖性限制过强。本文提出一族基于广义kappa-指数与kappa-对数函数的三参数非高斯概率密度函数,并研究其数学性质。该κ-对数正态密度为对数正态分布的连续变形,右尾更轻,由参数κ控制。特定参数组合下可产生双峰分布。我们推导了κ-对数正态分布主要统计函数的闭式解析表达式;对于矩,给出基于超几何函数的界及级数展开式。同时获得负对数似然梯度与海森矩阵的显式表达式,便于基于数据进行数值最大似然估计。还通过雅可比多变量定理,从潜在高斯过程构建κ-对数正态随机过程的联合概率密度函数。利用合成与真实数据验证了κ-对数正态分布的估计性能。进一步研究了在不同协方差核下的κ-对数正态过程在时间序列预测与空间插值中的应用,采用扭曲高斯过程回归方法。结果对各类科学与工程领域中偏态分布的建模具有实际意义。
原文摘要 · Abstract (English)
Asymmetric, non-Gaussian probability distributions are often observed in the analysis of natural and engineering datasets. The lognormal distribution is a standard model for data with skewed frequency histograms and fat tails. However, the lognormal law severely restricts the asymptotic dependence of the probability density and the hazard function for high values. Herein we present a family of three-parameter non-Gaussian probability density functions that are based on generalized kappa-exponential and kappa-logarithm functions and investigate its mathematical properties. These kappa-lognormal densities represent continuous deformations of the lognormal with lighter right tails, controlled by the parameter kappa. In addition, bimodal distributions are obtained for certain parameter combinations. We derive closed-form analytic expressions for the main statistical functions of the kappa-lognormal distribution. For the moments, we derive bounds that are based on hypergeometric functions as well as series expansions. Explicit expressions for the gradient and Hessian of the negative log-likelihood are obtained to facilitate numerical maximum-likelihood estimates of the kappa-lognormal parameters from data. We also formulate a joint probability density function for kappa-lognormal stochastic processes by applying Jacobi's multivariate theorem to a latent Gaussian process. Estimation of the kappa-lognormal distribution based on synthetic and real data is explored. Furthermore, we investigate applications of kappa-lognormal processes with different covariance kernels in time series forecasting and spatial interpolation using warped Gaussian process regression. Our results are of practical interest for modeling skewed distributions in various scientific and engineering fields.
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