/// <summary>Computes the RMSE fit of a recommender on the training data</summary>
/// <returns>the RMSE on the training data</returns>
/// <param name='recommender'>the rating predictor to evaluate</param>
public static double ComputeFit(this RatingPredictor recommender)
{
return(recommender.Evaluate(recommender.Ratings)["RMSE"]);
}