st: Is Stata smart enough to avoid unnecessary repetition?

[Richard Williams <Richard.A.Williams.5@nd.edu>]

Is Stata smart enough to know when it already has the necessary information 
calculated for an estimation command?  For example, if I do

regress y x1 x2 x3
regress y x1 x2 x3

will stata redo the regression or will it know that it has already done it 
and just replay the results?  Or, less obviously, if you do something like

regress y x1 x2 x3
pcorr y x1 x2 x3

the -pcorr- command will quietly regress y x1 x2 x3.  Will Stata do that 
regression anew or does it know it doesn't need to bother?

If Stata is smart enough to avoid repetition, will it also be smart enough 
to know that it must start from scratch if the data have been edited or 
changed?

Put another way, does it make any difference whether I just replay results 
(e.g. type -regress- with no arguments) as opposed to repeating the 
original complete command?

I've been using Stata with small data sets and it seems extremely 
fast.  But, I may start using it with some enormous data sets, and I'm also 
starting to write some ado files, and I'm wondering whether I have to worry 
about how efficient my commands are or if Stata will choose the optimal 
strategy.



-------------------------------------------
Richard Williams, Associate Professor
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