argument -i is mandatory 
ptaprune :      Builds and prune a PTA from a training set 

Usage : ptaprune -i Datas [-p PtaName] [-n nb] [-u unifile] [-e eps] [-h] 

Arguments : 

         -i Datas : Name of data file
         -p : prints the PTA and exit; PTA name : P
         -n : sets the number of states to prune
         -e : defines discounting value for smoothing. Default 0.6
         -u : defines the unigram to use. Estimate using the training set if not set
         -h : this help

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Example :

Using the ATIS data, to build the pta (no pruning) :

./ptaprune_linux_i586 -i atis -n 0  -p pta.txt 

The resulting pta is in the file pta.txt

To build the pta with 10000 states pruned :

./ptaprune_linux_i586 -i atis -n 10000  -p pta_pruned.txt