This function is similar to the CalibIX function, but instead of the
computed array, eventIX retrieves the index of the raw data array. The array to
which the index can be applied is IDATA(). Its purpose is to allow
looping in user routines when repetitive operations have to be done on
consecutive raw data words.
F The function name has to be declared as INTEGER*4 parameter.
index = eventIX (raw_data_name)