st: Looping over datetimes for simultaneous variable generation

[Paul Balcombe <paul.balcombe@postgrad.manchester.ac.uk>]

I have a timeseries data set and I want to generate a number of variables that are conditional on each other and their previous values, so I want to create a value for the set of variables at each time period in my data. I thought I should use a forvalues command, but this is new to me and I have so far been unsuccessful: invalid syntax. below is the command I wish to make:
 
forvalues datetime= ‘tc(19aug2012 00:00:00)’ (‘tc(00:05:00)’) ‘tc(18aug2013 23:00:00)’ { 
                replace seen=seen[_n-1] if seen==. & seen3[_n-1]<seen[_n-1]
                replace segaspow=segaspow[_n-1] if seen==. & seen3[_n-1]<seen[_n-1]
                replace seen2=seen2[_n-1] if seen==. & seen3[_n-1]<seen[_n-1]
                replace seen3=seen2+seen3[_n-1] if seen==. & seen3[_n-1]<seen[_n-1]
}
 
I may be describing the datetime functions incorrectly.
Thanks,
Paul
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