[amibroker] Re: Note about evaluation of formulas that assign Null (-1e10) value to some bar

["Bill Barnard" <wbarnard@xxxxxxx>]

Tomasz,

Thank you for the explanation. I worked on one of my formulas with
DeBugView for hours last night before finding the required fix. Now I
understand the 'why' of it.

The new features are terrific; I particularly like the chart timing
notification and the new color functions.

Bill


--- In amibroker@xxxxxxxxxxxxxxx, "Tomasz Janeczko" <amibroker@xxxx>
wrote:
>
> Hello,
> 
> 
> Note about evaluation of formulas that assign Null (-1e10) value to
some bars:
> 
> If your formula specifically assigns Null (-1e10) values to bars in
the middle or at the end of the data series
> it will be evaluated differently in 4.75.0 compared to 4.74.x and before
> 
> For example this code:
> 
> xx = IIf( BarIndex() > 10 AND BarIndex() < 100, C, Null );  // <-
NULL assigned at the end of series
> yy = 2 * xx; 
> 
> will result in yy being equal 2 * -1e10 = -2e10 instead of Null at
the end of the series.
> 
> In other words, Nulls propagate only if used at the beginning of the
series not at the end or middle.
> 
> If you have such codes in your formulas you have to rewrite it to:
> 
> good = BarIndex() > 10 AND BarIndex() < 100;
> xx = IIf( good, C, Null );  // <- NULL assigned at the end of series
> yy = IIF( good, 2 * xx, Null ); 
> 
> to exclude ending Null bars from evaluation.
> 
> This change was enforced by speed optimizations (checking for Nulls
for each bar in each operation is expensive
> - it requires more time than calculation itself, ie. multiplication
takes less than checks.)
>  
> Best regards,
> Tomasz Janeczko
> amibroker.com
>





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