def slope_statsample(xx, yy)
      sr = Statsample::Regression.simple(xx.to_scale, yy.to_scale)
      [sr.a, sr.b]
    end
def slope_statsample(xx, yy)
      sr = Statsample::Regression.simple(xx.to_scale, yy.to_scale)
      [sr.a, sr.b]
    end
Caclulates the slope of the regression line
 give a set of 2d coordonates of the start/stop offests of the hits
 Param
 xx : +Array+ of integers
 yy : +Array+ of integers
 Output:
 The ecuation of the regression line: [y slope]