code: func linearRegression(samples []Point, interceptTime int64) (slope, intercept float64) {
  	var (
  		n            float64
  		sumX, sumY   float64
  		sumXY, sumX2 float64
  	)
  	for _, sample := range samples {
  		x := float64(sample.T-interceptTime) / 1e3
  		n += 1.0
  		sumY += sample.V
  		sumX += x
  		sumXY += x * sample.V
  		sumX2 += x * x
  	}
  	covXY := sumXY - sumX*sumY/n
  	varX := sumX2 - sumX*sumX/n
  
  	slope = covXY / varX
  	intercept = sumY/n - slope*sumX/n
  	return slope, intercept
  }
docs: // linearRegression performs a least-square linear regression analysis on the
  // provided SamplePairs. It returns the slope, and the intercept value at the
  // provided time.