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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 prob

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vipul utsav
vipul utsav 2012-12-24
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

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Wayne King
Wayne King 2012-12-24
编辑：Wayne King 2012-12-24
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
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