Semisupervised Negative Correlation Learning

Negative correlation learning (NCL) is an ensemble learning algorithm that introduces a correlation penalty term to the cost function of each individual ensemble member. Each ensemble member minimizes its mean square error and its error correlation with the rest of the ensemble. This paper analyzes NCL and reveals that adopting a negative correlation term for unlabeled data is beneficial to improving the model performance in the semisupervised learning (SSL) setting. We then propose a novel SSL algorithm, Semisupervised NCL (SemiNCL) algorithm. The algorithm considers the negative correlation terms for both labeled and unlabeled data for the semisupervised problems. In order to reduce the computational and memory complexity, an accelerated SemiNCL is derived from the distributed least square algorithm. In addition, we have derived a bound for two parameters in SemiNCL based on an analysis of the Hessian matrix of the error function. The new algorithm is evaluated by extensive experiments with various ratios of labeled and unlabeled training data. Comparisons with other state-of-the-art supervised and semisupervised algorithms confirm that SemiNCL achieves the best overall performance.