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arXiv 1802.09022math.OCcs.CC
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无导数光滑随机凸优化的一种加速方法

An Accelerated Method for Derivative-Free Smooth Stochastic Convex Optimization

Eduard Gorbunov, Pavel Dvurechensky, Alexander Gasnikov

摘要:

我们考虑一个无约束的问题,最小化的光滑凸函数,这是唯一的,通过噪声观测其值,噪声由两部分组成。类似于随机最优化问题,第一部分是随机性的。第二部分是性质未知但有绝对值界的加性噪声。在两点反馈的设置,即当对函数值是可用的,我们提出了一个加速的导数自由算法及其复杂性分析。我们的无导数算法的复杂性界限仅比加速的基于梯度的算法的界限大$\sqrt{n}$倍,其中$n$是决策变量的维度。我们还提出了一个非加速无导数算法的复杂性界类似于随机梯度算法,即,我们的界没有任何维数依赖的因素,除了对数。值得注意的是,如果起始点和解之间的差是稀疏向量,对于我们的两个算法,如果算法使用$1$ -范数邻近设置,而不是欧几里德邻近设置,则我们获得更好的复杂度界,欧几里德邻近设置是无约束问题的标准选择

英文摘要:

We consider an unconstrained problem of minimizing a smooth convex function which is only available through noisy observations of its values, the noise consisting of two parts. Similar to stochastic optimization problems, the first part is of stochastic nature. The second part is additive noise of unknown nature, but bounded in absolute value. In the two-point feedback setting, i.e. when pairs of function values are available, we propose an accelerated derivative-free algorithm together with its complexity analysis. The complexity bound of our derivative-free algorithm is only by a factor of $\sqrt{n}$ larger than the bound for accelerated gradient-based algorithms, where $n$ is the dimension of the decision variable. We also propose a non-accelerated derivative-free algorithm with a complexity bound similar to the stochastic-gradient-based algorithm, that is, our bound does not have any dimension-dependent factor except logarithmic. Notably, if the difference between the starting point and the solution is a sparse vector, for both our algorithms, we obtain a better complexity bound if the algorithm uses an $1$-norm proximal setup, rather than the Euclidean proximal setup, which is a standard choice for unconstrained problems

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