MATLAB: Fun1= normrnd(20​,sqrt(0.6)​,[400 400]); fun1 = 20 + sqrt(0.6)*randn(400); in above function 20 is mean and 0.6 is a variance; fun1 should generate 20 mean and 0.6 variance matrix of 400*400 . but i got 20 mean and variance is 0.0018,,,so what is p

Question

fun1= normrnd(20,sqrt(0.6),[400 400]); fun1 = 20 + sqrt(0.6)*randn(400);

in above function 20 is mean and 0.6 is a variance; fun1 should generate 20 mean and 0.6 variance matrix of 400*400 . but i got 20 mean and variance is 0.0018,,,so what is problem for improper variance

Answer 1

   X = normrnd(20,sqrt(0.6),400,400);
   meanz = mean(X);
   varz = var(X);

I get approximately 20 as the mean of every column and 0.6 as the variance of every column

You cannot calculate the variance by

    var(var(X))

because the variance of the variances will not vary much! As expected

But not that

    mean(X(:))

and

    var(X(:))

give you the expected results