Interpreting GMStrings: The two characters between the colons

EYE uses data structures called kdtrees to make predictions more computationally efficient. The kdtrees can be used in three modes, indicated by the value of the first character between the colons:

• `S': slow mode; this is the most accurate mode and yields exactly the same answers as conventional predictions methods.
• `M': medium mode; this is almost as accurate as the slow mode, but runs more quickly.
• `F': fast mode; this gives less accurate (but still good) predictions and runs much more quickly.

The second character between the colons is usually set to `N' meaning that the time variable--if it is even included in the data--should not be treated specially. If time is included in the data, however, you may wish to set this character to `W'. EYE will then only use datapoints older than the current query point when making a prediction (i.e. it won't cheat and peer through a time portal into the future).

Returning to our example GMString, L24:SN:93-9, we now also know that the corresponding function approximator will use kdtrees in the slow but fully accurate mode, and that it will not treat time specially.

The default value for this pair of characters is `SN'. It is legal to omit this section of the GMString if it takes the default value. Thus our example, L24:SN:93-9, could be legally abbreviated as L24:93-9.