package indicator import ( "math" "github.com/c9s/bbgo/pkg/types" ) // Refer: https://easylanguagemastery.com/indicators/predictive-indicators/ // Refer: https://github.com/twopirllc/pandas-ta/blob/main/pandas_ta/overlap/ssf.py // Ehler's Super Smoother Filter // // John F. Ehlers's solution to reduce lag and remove aliasing noise with his // research in aerospace analog filter design. This indicator comes with two // versions determined by the keyword poles. By default, it uses two poles but // there is an option for three poles. Since SSF is a (Resursive) Digital Filter, // the number of poles determine how many prior recursive SSF bars to include in // the design of the filter. So two poles uses two prior SSF bars and three poles // uses three prior SSF bars for their filter calculations. // //go:generate callbackgen -type SSF type SSF struct { types.SeriesBase types.IntervalWindow Poles int c1 float64 c2 float64 c3 float64 c4 float64 Values types.Float64Slice UpdateCallbacks []func(value float64) } func (inc *SSF) Update(value float64) { if inc.Poles == 3 { if inc.Values == nil { inc.SeriesBase.Series = inc x := math.Pi / float64(inc.Window) a0 := math.Exp(-x) b0 := 2. * a0 * math.Cos(math.Sqrt(3.)*x) c0 := a0 * a0 inc.c4 = c0 * c0 inc.c3 = -c0 * (1. + b0) inc.c2 = c0 + b0 inc.c1 = 1. - inc.c2 - inc.c3 - inc.c4 inc.Values = types.Float64Slice{} } result := inc.c1*value + inc.c2*inc.Values.Index(0) + inc.c3*inc.Values.Index(1) + inc.c4*inc.Values.Index(2) inc.Values.Push(result) } else { // poles == 2 if inc.Values == nil { inc.SeriesBase.Series = inc x := math.Pi * math.Sqrt(2.) / float64(inc.Window) a0 := math.Exp(-x) inc.c3 = -a0 * a0 inc.c2 = 2. * a0 * math.Cos(x) inc.c1 = 1. - inc.c2 - inc.c3 inc.Values = types.Float64Slice{} } result := inc.c1*value + inc.c2*inc.Values.Index(0) + inc.c3*inc.Values.Index(1) inc.Values.Push(result) } } func (inc *SSF) Index(i int) float64 { if inc.Values == nil { return 0.0 } return inc.Values.Index(i) } func (inc *SSF) Length() int { if inc.Values == nil { return 0 } return inc.Values.Length() } func (inc *SSF) Last() float64 { if inc.Values == nil { return 0.0 } return inc.Values.Last() } var _ types.SeriesExtend = &SSF{} func (inc *SSF) calculateAndUpdate(allKLines []types.KLine) { if inc.Values != nil { inc.Update(allKLines[len(allKLines)-1].Close.Float64()) inc.EmitUpdate(inc.Last()) return } for _, k := range allKLines { inc.Update(k.Close.Float64()) inc.EmitUpdate(inc.Last()) } } func (inc *SSF) handleKLineWindowUpdate(interval types.Interval, window types.KLineWindow) { if inc.Interval != interval { return } inc.calculateAndUpdate(window) } func (inc *SSF) Bind(updater KLineWindowUpdater) { updater.OnKLineWindowUpdate(inc.handleKLineWindowUpdate) }