156,481 research outputs found
On optimal sequential prediction for general processes
In the stochastic sequential prediction problem, the elements of a random process X 1 , X 2 , ... 2 R are successively revealed to a forecaster. At each time t the forecaster makes a prediction F t of X t based only on X 1 , ..., X t 1 , when X t is revealed, the forecaster incurs a loss `(F t , X t ). This paper considers several aspects of the sequential prediction problem for unbounded, non-stationary processes under p-th power loss , 1 < p < 1. In the first part of the paper it is shown that Bayes prediction schemes are Cesaro optimal under general conditions, that Cesaro optimal prediction schemes are unique in a natural sense, and that Cesaro optimality is equivalent to a form of weak calibration. Extensions of the existence and uniqueness results to generalized prediction, and prediction from observations with additive noise, are established
Sequential Data-Adaptive Bandwidth Selection by Cross-Validation for Nonparametric Prediction
We consider the problem of bandwidth selection by cross-validation from a
sequential point of view in a nonparametric regression model. Having in mind
that in applications one often aims at estimation, prediction and change
detection simultaneously, we investigate that approach for sequential kernel
smoothers in order to base these tasks on a single statistic. We provide
uniform weak laws of large numbers and weak consistency results for the
cross-validated bandwidth. Extensions to weakly dependent error terms are
discussed as well. The errors may be {\alpha}-mixing or L2-near epoch
dependent, which guarantees that the uniform convergence of the cross
validation sum and the consistency of the cross-validated bandwidth hold true
for a large class of time series. The method is illustrated by analyzing
photovoltaic data.Comment: 26 page
Efficient Robust Optimization of Metal Forming Processes using a Sequential Metamodel Based Strategy
The coupling of Finite Element (FE) simulations to mathematical optimization techniques has contributed significantly to product improvements and cost reductions in the metal forming industries. The next challenge is to bridge the gap between deterministic optimization techniques and the industrial need for robustness. This paper introduces a new and generally applicable structured methodology for modeling and solving robust optimization problems. Stochastic design variables or noise variables are taken into account explicitly in the optimization procedure. The metamodel-based strategy is combined with a sequential improvement algorithm to efficiently increase the accuracy of the objective function prediction. This is only done at regions of interest containing the optimal robust design. Application of the methodology to an industrial V-bending process resulted in valuable process insights and an improved robust process design. Moreover, a significant improvement of the robustness (> 2s ) was obtained by minimizing the deteriorating effects of several noise variables. The robust optimization results demonstrate the general applicability of the robust optimization strategy and underline the importance of including uncertainty and robustness explicitly in the numerical optimization procedure
Nonparametric sequential prediction for stationary processes
We study the problem of finding an universal estimation scheme
, which will satisfy
\lim_{t\rightarrow\infty}{\frac{1}{t}}\sum_{i=1}^t|h_
i(X_0,X_1,...,X_{i-1})-E(X_i|X_0,X_1,...,X_{i-1})|^p=0 a.s. for all real valued
stationary and ergodic processes that are in . We will construct a single
such scheme for all , and show that for mere integrability
does not suffice but does.Comment: Published in at http://dx.doi.org/10.1214/10-AOP576 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
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