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As a general rule I use loops when
1. Existing AB functions cannot fulfil requirements.
eg use of AMA, Zig, Cum, or ApplyStop functions, or one of the
many others available
2. The current bar value of a variable is calculated using the
previous bar value of that same variable.
eg EMA if that was not already a built in function in AB
3. The value of a variable is determined from a specific occurrence of
a true condition, where that condition can have true values after that
specific occurrence.
eg trail stop value after Buy signal, that is not one of the
existing ApplyStop function possibilities.
This could be one that if could write simply would be
HighestSince( Buy, H - ATR( 10 ) ), but this gets reset by any
subsequent buy signals that you may not want to remove
AB Applystop (ModePoint) currently has 2 possibilities if
my memory is correct, they are
A: Non-Volatile HighestSince( Buy, H ) - ValueWhen(
buy, ATR( 10 ) ); and
B: Volatile HighestSince( Buy, H ) - ATR( 10 );
These bits of code would vary if you have a entry delay after signal.
4. Loop through a set number series that have no direct relation to
bar array identification as normally used in bar loops
eg for( n=1; n<=5; n=n+2 )
5. Probably some others as well, but have written so many cannot
always remember everything.
Hopefully my examples of code above are correct, I just typed them
into here from my poor memory
--
Cheers
Graham Kav
AFL Writing Service
http://www.aflwriting.com
2009/2/20 richpach2 <richpach2@xxxxxxxxx>:
> Hello,
>
> Can some please expain use of loop (if, while etc) expression in AFL?
> When do one need to use a loop and when can one just rely on
> processing of the array bar-by-bar. I am still learining AFL language
> and this area is a bit grey.
>
> I noticed many Stop processing AFL use "for" loop but I don't
> understand why.
> Also, if I can use this statement toi define EMA;
>
> P = ParamField("Price field",-1);
> Periods = Param("Periods", 15, 2, 300, 1, 10 );
> Plot( EMA( P, Periods ), _DEFAULT_NAME(), ParamColor( "Color",
> colorCycle ), ParamStyle("Style") );
>
> why would I try this AFL doc example;
>
> myema[ 0 ] = Close[ 0 ];
> for( i = 1; i < BarCount; i++ )
> {
> myema[ i ] = 0.1 * Close[ i ] + 0.9 * myema[ i - 1 ];
> }
> This example iterates all bars of close array to calculate
> exponential moving average.
>
> Regards
> Richard
>
>
>
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