Not all indicators are open source, some are under license. But here's the Lowpass filter:

Code:
var LowPass(var *data,int period)
{
	var* LP = series(*data,3);
	var a = 2./(period+1);
	var a2 = a*a;
	return LP[0] = (a-a2/4)*data[0]
		+ 0.5*a2*data[1]
		- (a-0.75*a2)*data[2]
		+ 2*(1.-a)*LP[1]
		- (1.-a)*(1.-a)*LP[2];
}