Mulloy's Double EMA: 2*EMA - EMA(EMA).
Center of mass. Exclusive with span/halflife/alpha.
Span (default smoothing parameter).
Halflife.
Smoothing parameter.
https://screamer.readthedocs.io/en/latest/ for the Python reference and full details.
Mulloy's Double EMA: 2*EMA - EMA(EMA).