get_Trace allows this user to recover the data from a DATA structure given the station name,components
channel name

Inputs:
DATA: structure returned by get_DATA, contains all the data from an extractet events (required)
station: station name (required)
channel cell: cell containing desired channel {‘SL’ ‘SH’} (optionnal)
components cell: cell containing desired channel {‘Z’ ‘X’} (optionnal)

  ex: get_TRACE(DATA,'DANN','chan','SL') returns all components associated to channel SL   
      get_TRACE(DATA,'DANN','chan','SL','comp','X') returns only X component (if exists) ass. to channel SL   

Outputs:
comp_select: cell with comp
chan_select: “”
trace_select: cell with data
trace_matrix: matrix with data