I'm getting negative numbers from using $stopwatch differences, could there be some sort of underflow problem? What I do is a typical simulation exercise: set stopwatch t_sim1 = 0 loop for simrun=1..replications --quiet <create random numbers> loop for t=1..T --quiet <do stuff with random numbers> start = $stopwatch <do more stuff> stop = $stopwatch <do more stuff> t_sim1 += stop-start end loop # t end loop # simrun print t_sim1 And t_sim1 is reproducibly negative.

On Thu, 30 Apr 2009, Allin Cottrell wrote: > On Thu, 30 Apr 2009, Sven Schreiber wrote: > >> I'm getting negative numbers from using $stopwatch differences, >> could there be some sort of underflow problem? >> >> What I do is a typical simulation exercise: >> >> set stopwatch >> t_sim1 = 0 >> loop for simrun=1..replications --quiet >> <create random numbers> >> loop for t=1..T --quiet >> <do stuff with random numbers> >> start = $stopwatch >> <do more stuff> >> stop = $stopwatch >> <do more stuff> >> t_sim1 += stop-start >> end loop # t >> end loop # simrun >> print t_sim1 >> >> And t_sim1 is reproducibly negative. Ah, I tried this again using an exact copy of your script with <stuff> filled in, and I did indeed get negative values of t_sim1. I was bothered at first, but then realized that's perfectly OK. I'd failed to notice the problem in your script. As per the manual, $stopwatch gives you the time _elapsed_ since "set stopwatch", or since the previous call to $stopwatch. Your calls start = $stopwatch ... stop = $stopwatch ... t_sim1 += stop-start seem to be assuming that $stopwatch gives you the current time, not the elapsed time: you want t_sim1 += $stopwatch.