After dividing dataset to train, validation and test set I use validation set to determine the best hyperparameters. After that I need to evaluate performance on test set. For this evaluation do I use merged train and validation set or just train set for training?
And how is this done if dataset is divided into train, test set and use crossvalidation on train set to find the best parameters? Here I probably use all train set for training final model and then test on test set?