Root mean-squared error (RMSE) is the square root of the average squared difference between predicted and observed values. It condenses forecast errors into one validation metric, while still requiring inspection of where predictions diverge. section 8.1.2
Stock-price validation
A random-forest model predicts the next trading day’s closing price from historical Open, High, Low, Close, and Volume data. After an 80/20 chronological split, RMSE is calculated from test-set predictions and actual prices; a plot reveals that forecast accuracy varies across dates. section 8.1.2






