hma(src, len, _id) {
        let id = this._tsid(_id, `hma(${len})`)
        let len2 = Math.floor(len/2)
        let len3 = Math.round(Math.sqrt(len))

        let a = this.mult(this.wma(src, len2, id+'1'), 2, id)
        let b = this.wma(src, len, id+'2')
        let delt = this.sub(a, b, id+'3')

        return this.wma(delt, len3, id+'4')
    }
Hull Moving Average
@param {TS} src - Input
@param {number} len - Length
@return {TS} - New time-series