* indw = 'w' if the date is given as a day date but corresponds to a week (optional)
Output
* num = the numerical representation of the dates
DESCRIPTION
Transforms a date into its numerical representation.
EXAMPLE
d=date2num('1985q4')// returns the numerical representation of the quarterly date '1985q4'd=date2num('2002a')// returns the numerical representation of the yearly date '2002a'.d=date2num('97m12')// returns the numerical representation of the monthly date '97m12'.d=date2num('2002/03/15','w')// returns the numerical representation of the daily date '2000/03/15'.