rand:0-1均匀分布.均值m=(a+b)/2; 方差=(b-a).^2/12;
randn:0均值,方差1.
只有当rand和randn生成较大的数据时,均值和方差才会成立.比如N>100
样例:
a = randn(10000,1);
mean(a(:)) = 0.0033
std(a(:)) = 1.0011
b = rand(10000,1);
mean(b(:)) = 0.5014
std(b(:)) = 0.2891
备注:sqrt(1/12) = sqrt((1-0)/12) = 0.2887
原文：http://www.cnblogs.com/qqhfeng/p/3561363.html