statisticsPen.py 文件源码

def __update(self):

        area = self.area
        if not area:
            self.__zero()
            return

        # Center of mass
        # https://en.wikipedia.org/wiki/Center_of_mass#A_continuous_volume
        self.meanX = meanX = self.momentX / area
        self.meanY = meanY = self.momentY / area

        #  Var(X) = E[X^2] - E[X]^2
        self.varianceX = varianceX = self.momentXX / area - meanX**2
        self.varianceY = varianceY = self.momentYY / area - meanY**2

        self.stddevX = stddevX = math.copysign(abs(varianceX)**.5, varianceX)
        self.stddevY = stddevY = math.copysign(abs(varianceY)**.5, varianceY)

        #  Covariance(X,Y) = ( E[X.Y] - E[X]E[Y] )
        self.covariance = covariance = self.momentXY / area - meanX*meanY

        #  Correlation(X,Y) = Covariance(X,Y) / ( stddev(X) * stddev(Y) )
        # https://en.wikipedia.org/wiki/Pearson_product-moment_correlation_coefficient
        correlation = covariance / (stddevX * stddevY)
        self.correlation = correlation if abs(correlation) > 1e-3 else 0

        slant = covariance / varianceY
        self.slant = slant if abs(slant) > 1e-3 else 0