Matconvnet中imagenet的getImageStart.m代码中求协方差的代码及均值（1，3）

分享一段代码，个人觉得比较好：

z = reshape(shiftdim(data,2),3,[]) ;rgbm1{end+1} = mean(z,2) ;rgbm2{end+1} = z*z'/size(z,2) ;avg{end+1} = mean(data, 4) ;averageImage = gather(mean(cat(4,avg{:}),4)) ;rgbm1 = gather(mean(cat(2,rgbm1{:}),2)) ;    % gather将数据转化为cpu数据rgbm2 = gather(mean(cat(3,rgbm2{:}),3)) ;rgbMean = rgbm1 ;rgbCovariance = rgbm2 - rgbm1*rgbm1' ;

data是一批彩色图像的矩阵！