NARX - Training/V​alidation/​Testing, group all testing to end of dataset

Hi All,

I have been using the "NTSTOOL" GUI to setup a prediction model in Matlab. For now I have used the default 70/15/15 split which results in a reasonable plot showing the points that have bene used for training/validation/testing.

I would like to know if anyone knows of a method to force the testing points to only occur in the final 15% of the dataset. Rather than scatter testing throughout the series, i would to aggregate the testing points to all occur in the final rows of my data set. Eg I would like the final 15% of my dataset to be used as the prediction.

I am new to Matlab so apologies if this question is basic. I have been reading through community posts but cant seem to find anything that discusses grouping the testing points together.

Many thanks!