论文标题
跨凝结方法用于优化
Cross-Entropy Method Variants for Optimization
论文作者
论文摘要
横向透镜(CE)方法是一种流行的随机方法,可以优化其简单性和有效性。 CE方法专为发生目标事件的概率相对较小而设计的稀有事实模拟依赖于足够的客观函数调用来准确估计基础分布的最佳参数。某些目标函数在计算上的评估可能很昂贵,并且CE方法可能会陷入本地最小值。这与必须具有足够宽的初始协方差以覆盖感兴趣的设计空间的需要更加复杂。我们介绍了CE方法的新型变体,以解决这些问题。为了减轻昂贵的功能调用,在优化期间,我们使用每个样本来构建一个替代模型来近似目标函数。替代模型通过较便宜的评估增强了目标函数的信念。我们为替代模型使用高斯流程将不确定性纳入预测中,这在处理稀疏数据时特别有用。为了解决当地的最小收敛,我们使用高斯混合模型来鼓励探索设计空间。当协方差最大时,我们尝试在优化中早些时候在优化中重新分配真正的目标函数调用,以实验评估调度技术。为了测试我们的方法,我们使用许多局部最小值和一个全局最小值创建了一个参数化的测试目标函数。可以调整我们的测试功能以控制最小值的扩散和区别。运行实验以强调跨凝结方法变体,结果表明,基于替代模型的方法可以使用相同数量的函数评估来降低局部最小值收敛。
The cross-entropy (CE) method is a popular stochastic method for optimization due to its simplicity and effectiveness. Designed for rare-event simulations where the probability of a target event occurring is relatively small, the CE-method relies on enough objective function calls to accurately estimate the optimal parameters of the underlying distribution. Certain objective functions may be computationally expensive to evaluate, and the CE-method could potentially get stuck in local minima. This is compounded with the need to have an initial covariance wide enough to cover the design space of interest. We introduce novel variants of the CE-method to address these concerns. To mitigate expensive function calls, during optimization we use every sample to build a surrogate model to approximate the objective function. The surrogate model augments the belief of the objective function with less expensive evaluations. We use a Gaussian process for our surrogate model to incorporate uncertainty in the predictions which is especially helpful when dealing with sparse data. To address local minima convergence, we use Gaussian mixture models to encourage exploration of the design space. We experiment with evaluation scheduling techniques to reallocate true objective function calls earlier in the optimization when the covariance is the largest. To test our approach, we created a parameterized test objective function with many local minima and a single global minimum. Our test function can be adjusted to control the spread and distinction of the minima. Experiments were run to stress the cross-entropy method variants and results indicate that the surrogate model-based approach reduces local minima convergence using the same number of function evaluations.