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Hello Barry
Thankyou for the heads up on this issue - your valuable experience and comments are much appreciated.
As for your comments regarding a way of devising a dynamic way of accessing eaqrlier bars using standard AFL logic would be ideal, but I am trying to resolve a problem with a trailing stop which I refered to in message 138653 Re: Trailing Stop S & C tips 1-2008 & 138598 Trailing Stop S & C tips 1-2008
All the trailing stops I have seen in AB seem to fall back on using flow control structures such as "for i = " loops to ratchet the stop.
In this case it requires a starting point at a given date on the chart applying a stop value on that date to start the calculation (ie access to an array element).
If there is a way of using AFL array logic to circumvent array element manipulation,I am open to suggestion.
Thank again for your input and other suggestions that you have regarding my comments above are most welcome.
Cheers
Ed
--- In amibroker@xxxxxxxxxxxxxxx, "Barry Scarborough" <razzbarry@xxx> wrote:
>
> Unless you specify SetBarsRequired(nnnn,nnnn) where nnnn is larger than the number of bars in your database Ami will only load enough bars, into a temporary array, so that it can display your charts correctly. When you add more bars to a window the temp array is enlarged and the indicator is recalculated so that what is plotted will again be correct. So the number you get in your test will be the number of bars displayed + the longest period in any of your indicators. It gets worse. If you try to manually access data that is beyond the scope of the temporary array you will get an access violation which will either blow your program up or return invalid data.
>
> There is another thing you need to know. When you set anything in an array you will have to set it every time the indicator is scanned. When the indicator is scanned all the indicators plotted are recalculated. In real time trading this can be many times a second and since you will be adding data the point you want to access may be outside the scope of the bars. If you are using static data it will scan your indicator every time you click on a bar or change the number of bars displayed or scroll through the bars. Managing data as you plan will get very complicated and hell to debug when it works incorrectly. Expect errors.
>
> You will be much better off if you can devise a dynamic way to access data in earlier bars using standard AFL logic. Then reference it with the Ref() statement. I see some people using for, do and while loops in Ami. Most of the time that can be replaced with AFL array logic which is much faster and less prone to calculation errors. For example someone sent me a formula the other day to debug. It was using all the bars in the ticker. I was testing an auto trading formula on a 5 minute chart and when I started his formula Ami ground to a crawl. It was processing his loop three times a second, well it was trying to and doing badly. Avoid loops wherever possible.
>
> Barry
>
> --- In amibroker@xxxxxxxxxxxxxxx, "edwol53" <edwol@> wrote:
> >
> > Hello
> >
> > I am trying to access/extract a subscript [i] if an array element a[i].
> >
> > The aim is to input a date and extract the bar subscript from that date's bar so that the subscript can be used over-write/modify an associated array element[i] (if I understand how array data is constructed in AFL correctly ???)
> >
> > A test code segment and debug outputis shown below. The issue I am having difficulty with is that in the first line the index and barcount are correct if all the data (including bars not displayed on the screen) is taken into account. In line 2 the barcount readjusts to number of bars displayed on the screen. I can accept that as a quirk but works. I then zoom out (as shown by barcount)loading all the bars (data) onto the screen(debug shows zoomout effect in line 9 - 26. But the subscript [i] is now empty from line 20 - as I continue to zoom out on the chart. Why?
> >
> > Is this a bug or is there something I am missing??
> >
> > Can anyone offer an explanation as to what is happening?
> >
> > // Array or number ?
> > dt = ParamDate("Date of the trend", "2009-05-25" ,0);
> > i=0;
> > i = ValueWhen(DateNum() == dt, BarIndex(), 1);
> >
> > _TRACE(" i = " + NumToStr(i, 1.0) + " index date = " + NumToStr(dt, 1.0) + " Barcount = " + NumToStr(BarCount, 1.0) );
> >
> > 00000000 0.00000000 [2440] i = 6,413 index date = 1,090,525 Barcount = 6,416
> > 00000001 0.03319501 [2440] i = 6,413 index date = 1,090,525 Barcount = 69
> > 00000002 2.32265329 [2440] i = 6,413 index date = 1,090,525 Barcount = 69
> > 00000003 7.29352045 [2440] i = 6,413 index date = 1,090,525 Barcount = 69
> > 00000004 12.29429150 [2440] i = 6,413 index date = 1,090,525 Barcount = 69
> > 00000005 17.29241562 [2440] i = 6,413 index date = 1,090,525 Barcount = 69
> > 00000006 22.29343414 [2440] i = 6,413 index date = 1,090,525 Barcount = 69
> > 00000007 27.29189682 [2440] i = 6,413 index date = 1,090,525 Barcount = 69
> > 00000008 32.29233551 [2440] i = 6,413 index date = 1,090,525 Barcount = 69
> > 00000009 36.40725327 [2440] i = 6,413 index date = 1,090,525 Barcount = 92
> > 00000010 36.77444458 [2440] i = 6,413 index date = 1,090,525 Barcount = 127
> > 00000011 37.05470276 [2440] i = 6,413 index date = 1,090,525 Barcount = 179
> > 00000012 37.29121780 [2440] i = 6,413 index date = 1,090,525 Barcount = 179
> > 00000013 37.30448532 [2440] i = 6,413 index date = 1,090,525 Barcount = 257
> > 00000014 37.54277802 [2440] i = 6,413 index date = 1,090,525 Barcount = 374
> > 00000015 37.72683716 [2440] i = 6,413 index date = 1,090,525 Barcount = 550
> > 00000016 37.91091156 [2440] i = 6,413 index date = 1,090,525 Barcount = 814
> > 00000017 38.09486389 [2440] i = 6,413 index date = 1,090,525 Barcount = 1,210
> > 00000018 38.33518219 [2440] i = 6,413 index date = 1,090,525 Barcount = 1,804
> > 00000019 39.79113770 [2440] i = 6,413 index date = 1,090,525 Barcount = 2,695
> > 00000020 40.27950287 [2440] i = {EMPTY} index date = 1,090,525 Barcount = 4,031
> > 00000021 40.58501816 [2440] i = {EMPTY} index date = 1,090,525 Barcount = 6,035
> > 00000022 40.80830765 [2440] i = {EMPTY} index date = 1,090,525 Barcount = 6,416
> > 00000023 42.29502487 [2440] i = {EMPTY} index date = 1,090,525 Barcount = 6,416
> > 00000024 47.29590988 [2440] i = {EMPTY} index date = 1,090,525 Barcount = 6,416
> > 00000025 52.29293823 [2440] i = {EMPTY} index date = 1,090,525 Barcount = 6,416
> > 00000026 57.29567719 [2440] i = {EMPTY} index date = 1,090,525 Barcount = 6,416
> >
>
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