st: replacing values in panel data

[billy mairs <mairs8@hotmail.com>]

Dear reader, 

I have a panel data set and wish to replace multiple values over the different cross sections.
 
Say the panel data is N=20 and T=5. I have 5 values for a standard normal error term ‘u’ (for every t) for my first panel, say i = 1. I want to copy these 5 values into the other cross section units, so that u is the same in the other 19 panels as it is in my first panel. Here is what I have come up with so far
 
clear all
set obs 20
gen i = _n
expand 5
sort i
by i: gen t=_n
tsset i t
gen x = rnormal()
gen u = rnormal() in 1/5
br
 
How would I then copy the values for u into the missing values so that at each t, u is the same across the panels?
I hope to then use the command
 
replace u = (0.5)*u + ((1-0.25)^0.5)*rnormal() if i>1
 
in order to create dependence in error terms across the panels. Thanks for your time 		 	   		  
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