Trains a Prediction by Partial Match (PPM) model from a collection of sequences. 

$USAGE$
<modelname> the name of the PPM model
<sequences> the name of the sequences from which the model is trained
<probEscape> defines the probability to use a lower order Markov model
<maxOrder> defines the Markov order of the PPM model
<minOrder> optional; defines the minimal Markov order of the PPM model; default: 0

Examples:
trainPPM ppm sequences 0.1 3
trainPPM ppm sequences 0.1 3 1