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Thanks for all help on handling the automatica maxbarsback.
Everybody are in agreement: If using printing/fileappend, turn auto off.
Speeds up your system, assures correct output and any problems during
workchart scanning will be reported.
So now I know what to do the coming weeks...
> -----Original Message-----
> From: Gary Fritz [mailto:fritz@xxxxxxxx]
> Sent: den 4 april 2001 18:44
> To: omega-list@xxxxxxxxxx
> Subject: Re: needing help and advice on maxbarsback
>
>
> > (My belief is that a maxbarsback of auto just means Tradestation
> > first tries with a low number, when it hits a problem with that
> > number it increases maxbarsback and then tries again). This is
> > correct?
>
> That's exactly what happens. You can see this happening if you print
> the bar date/time/number on each bar, then go through the print log.
> You'll see it start at the first bar, go through some number of bars
> until it hits the MBB limit, then it goes back to the start with a
> larger MBB. It may do this many times, depending on the study.
>
> Obviously that will totally mess up any data you write to files.
>
> > Anyone know the algorithm for how it increases maxbarsback?
>
> I don't know the precise algorithm, but you can infer it.
>
> I applied this indicator to a daily chart, with MBB set to "Auto":
>
> fileappend("e:\temp\foo.txt",
> numtostr(d,0) & ": BarNumber = " & numtostr(BarNumber,0)
> & newline);
> value1 = highest(high, BarNumber);
> if false then plot1(0,"");
>
> The file shows that barnumber went from 1 to 3, then 1-5, then 1-7, 1-
> 9, 1-11, 1-13, 1-15 ... I think I see a pattern forming here. :-)
>
> If I change the lookback to highest(high,10*BarNumber), the first few
> lines look like this:
>
> 980730: BarNumber = 1
> 980812: BarNumber = 1
> 980813: BarNumber = 2
> 980826: BarNumber = 1
> 980827: BarNumber = 2
> 980828: BarNumber = 3
> 980910: BarNumber = 1
> 980911: BarNumber = 2
> 980914: BarNumber = 3
> 980915: BarNumber = 4
> 980924: BarNumber = 1
> 980925: BarNumber = 2
> 980928: BarNumber = 3
> 980929: BarNumber = 4
> 980930: BarNumber = 5
> 981008: BarNumber = 1
> 981009: BarNumber = 2
> 981012: BarNumber = 3
> 981013: BarNumber = 4
> 981014: BarNumber = 5
> 981015: BarNumber = 6
> 981022: BarNumber = 1
>
> So it appears to be jumping MBB by about 10 each time. It looks like
> the algorithm is somewhat adaptive.
>
> Notice, BTW, that the date on BarNumber 1 **changes** each time.
> That's because BarNumber = 1 is NOT the first bar of the chart, but
> the MaxBarsBack+1 bar. 980730 is actually the 2nd bar on the chart,
> so MBB was 1 on the first attempt. 980812 is the 11th bar, so MBB
> was 10 on the 2nd attempt. 980826 was the 21st bar, 980910 was the
> 31st bar, etc.
>
> If I was to guess, I would say TS is increasing MBB just enough to
> cover the case that just exceeded the old MBB. E.g. the first pass
> had MBB = 1, but I looked back 10*BarNumber or 10. So it set it to
> 10 on the second attempt.
>
> > Now, when I am planning to change this setting, I am afraid of
> > causing errors that I do not have today.
>
> If you understand your indicators, you know how far back they can go.
> Set MBB to that value.
>
> If your indicators have an unbounded lookback -- e.g. if they store
> the last high swing, and then do a highest(High,LastSwing) or
> something like that -- you can usually rewrite them to avoid the
> lookback. You'll limit your unbounded lookback and the indicator
> will be more efficient in the bargain. (Of course, efficiency is
> probably not a key concern if you're dumping stuff to files.)
>
> > The manual recommends to always set it to at least 50. Why? I can
> > not see any good reason?
>
> It's just a reasonable starting point that covers common usage
> patterns for most users. There's no need to set it that high if you
> don't need it. E.g. let's say you have an indicator that does an
> xaverage, and nothing else that looks into history. You could
> actually set MBB to 1 because xaverage only looks back 1 bar.
>
> > If using the workchart assistant for scanning a lot of stocks and
> > having a maxbarsback setting that is too low, will I ever get an
> > error message telling me if maxbarsback is too low? Or will I just
> > have a number of indicators that did not deliver data for some
> > stocks? Or was even turned off? Anyone could give me some hints on
> > this?
>
> You'll get an error. Like I said, you need to look at your indicator
> to see how far back it actually can look. If it's unbounded, rewrite
> the indicator to limit the lookback.
>
> Gary
>
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