public static function subtract($ts = null, $num = 1, $unit = sfTime::DAY)
	{
		return sfTime::add($ts, $num * -1, $unit);
	}
public static function subtract($ts = null, $num = 1, $unit = sfTime::DAY)
	{
		return sfTime::add($ts, $num * -1, $unit);
	}
public static function subtract ( $ ts = null , $ num = 1 , $ unit = sfTime :: DAY ) { return sfTime :: add ( $ ts , $ num * - 1 , $ unit ) ; }
Subtracts the specified number of given units of time from the given date.

<b>Example:</b>
<code>
// yesterday
$dt = sfTime::subtract();
// day before
$dt = sfTime::subtract($mydate);
// 5 days before
$dt = sfTime::subtract($mydate, 5);
// 2 months before
$dt = sfTime::subtract($mydate, 2, sfTime::MONTH);
// 4 weeks before
$dt = sfTime::subtract($mydate, 4, sfTime::WEEK);
</code>

@param	timestamp	a timestamp for the calculation
@param	int			the number of units to add to the given date
@param	int			the unit to add by
@return	timestamp	the timestamp result of the calculation

@see		add
Subtracts the specified number of given units of time from the given date .