inv_yhat = scaler.inverse_transform(inv_yhat)

This line of code is used to invert the scaling applied to the predicted values (inv_yhat). In machine learning models, it is common to apply feature scaling to the input data before training the model. This is done to normalize the data and improve the performance of the model. However, the predicted values are also scaled and need to be inverted to their original scale before they can be compared to the actual values.

In this case, the "scaler" object is a scaler that was used to normalize the data before training the model. The "inverse_transform" method of the scaler is used to invert the scaling applied to the predicted values (inv_yhat) and convert them back to their original scale. The resulting values are then stored in the "inv_yhat" variable.