linreg(src, len, offset = 0, _id) {
        let id = this._tsid(_id, `linreg(${len})`)

        src.__len__ = Math.max(src.__len__ || 0, len)
        let lr = linreg(src, len, offset)

        return this.ts(lr, id, src.__tf__)
    }
Linear Regression
@param {TS} src - Input
@param {number} len - Length
@param {number} offset - Offset
@return {TS} - New time-series