*3.6. Evaluation*

Forecasting performance was evaluated using three performance evaluation metrics, namely, mean absolute error (MAE) [39], RMSE [40], and NRMSE [39]. They are defined as follows:

$$\text{MAE} = \frac{1}{N} \sum\_{i=1}^{N} |\mathcal{G}\_i - y\_i| \tag{1}$$

$$\text{RMSE} = \sqrt{\frac{\sum\_{i=1}^{N} (\mathcal{Y}\_i - y\_i)^2}{N}} \tag{2}$$

$$\text{NRMSE} = \frac{\sqrt{\frac{\sum\_{i=1}^{N} (y\_i - y\_i)^2}{N}}}{\mu} \tag{3}$$

$$\text{NRMSE}(\%) = \frac{\sqrt{\frac{\sum\_{i=1}^{N} (\hat{y}\_i - y\_i)^2}{N}}}{\mu} \ast 100\% \tag{4}$$
