p300 wave feature extraction matlab code

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Hello everyone,
We are interested in performing a P300 session . We are using G.Recorder software to view the EEG data along with the trigger. The trigger(1 Hz frequency) is generated from the signal generator. We have also generated our own stimulus, which is the random presentation of numbers from 0-9.
Now our task is to write a MATLAB code to extract the P300 wave. It would be very helpful to us if someone would guide us towards the process of writing the code , or providing us with an algorithm .

Thank you in advance.
Awaiting your reply,
Manjusha and Ashwini.