fit_linear

# File lib/minitest/benchmark.rb, line 247
    def fit_linear xs, ys
      n   = xs.size
      xys = xs.zip(ys)
      sx  = sigma xs
      sy  = sigma ys
      sx2 = sigma(xs)  { |x|   x ** 2 }
      sxy = sigma(xys) { |x,y| x * y  }

      c = n * sx2 - sx**2
      a = (sy * sx2 - sx * sxy) / c
      b = ( n * sxy - sx * sy ) / c

      return a, b, fit_error(xys) { |x| a + b * x }
    end