grouped data: generating a random error with zero group mean

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Rabeya
Rabeya 2012-4-22
I have a variable 'group' with 20 distinct values randomly assigned for 8000 observations. I need to generate a random error term,u, with zero mean in each group, and a specific covariance, say 10. how to do that?
I can do for an overall zero mean, as
u = random('Normal',0,10,length(group),1)
but not for zero group means.

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Tom Lane
Tom Lane 2012-4-22
Your code generates each observation from a theoretical distribution that has zero mean. Consequently the theoretical mean is zero overall, and within each group. Can you describe more specifically what you need beyond this?

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