GeneticKNN: a weighted KNN approach supported by genetic algorithm for photometric redshift estimation of quasars

Abstract

Abstract We combine K-nearest neighbors (KNN) with a genetic algorithm (GA) for photometric redshift estimation of quasars, short for GeneticKNN, which is a weighted KNN approach supported by a GA. This approach has two improvements compared to KNN: one is the feature weighted by GA; the other is that the predicted redshift is not the redshift average of K neighbors but the weighted average of median and mean of redshifts for K neighbors, i.e. p × z median + (1 – p) × z mean. Based on the SDSS and SDSS-WISE quasar samples, we explore the performance of GeneticKNN for photometric redshift estimation, comparing with the other six traditional machine learning methods, i.e. the least absolute shrinkage and selection operator (LASSO), support vector regression (SVR), multi-layer perceptrons (MLP), XGBoost, KNN and random forest. KNN and random forest show their superiority. Considering the easy implementation of KNN, we make improvement on KNN as GeneticKNN and apply GeneticKNN on photometric redshift estimation of quasars. Finally the performance of GeneticKNN is better than that of LASSO, SVR, MLP, XGBoost, KNN and random forest for all cases. Moreover the accuracy is better with the additional WISE magnitudes for the same method.