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Barry,
PREV is NOT ref(c,-1) in this example but yesterday's value of Z. Otherwise
PREV wouldn't be necessary im Metastock since MS has the same ref function
like Amibroker.
Regards,
Thomas
On 07.07.2009, 02:36:10 Barry Scarborough wrote:
> If PREV works only on C in the example, wouldn't this run faster than using
> a loop in AFL? Z =(A*B)+(C*Ref(C,-1)); Unless something has changed in the
> latest AFL releases Tomasz's array processing is much faster than using
> loops to perform the same function in AFL.
>
> Barry
>
> --- In amibroker@xxxxxxxxxxxxxxx, Thomas Ludwig <Thomas.Ludwig@xxx> wrote:
> > Hello,
> >
> > TJ once wrote:
> >
> > [quote]
> > Hello,
> >
> > PREV in MS is needed because MS does NOT have looping.
> >
> > In AB, there are loop constructs so there is no need for PREV
> > because loops give faster and more general way of solving coding
> > problems.
> >
> > Since loops are more general they allow easy translation of every
> > case where MS needs PREV.
> >
> > Statment like this:
> > Z =(A*B)+(C*PREV);
> >
> > Using loop looks as follows:
> >
> > z = 0; // initialize
> > for( i = 1; i < BarCount; i++ )
> > {
> > prev = Z[ i - 1 ]; // PREV is previous value of Z.
> > Z[ i ] = A[ i ] * B[ i ] + C[ i ] * prev;
> > }
> >
> > As you can see the statement is identical with the exception that
> > AFL looping code uses [ ] operator to access individual array elements.
> >
> > Good thing is that AFL looping code is BarCount-times faster than MS
> > code. Since 5 years of EOD data is 1300 bars, AFL looping code is 1300
> > times faster than MS in that case.
> >
> > It is also possible to use AMA/AMA2 instead of PREV:
> >
> > Z = AMA2( A, B, C );
> >
> > which is shorter but AMA is less general than looping code.
> > [/quote]
> >
> > HTH
> >
> > Greetings,
> >
> > Thomas
> >
> > On 15.06.2009, 13:06:00 Mubashar virk wrote:
> > > Hi all,
> > >
> > > Has any one worked out a universal AFL Function = the perversity in
> > > MetaStock that is called PREV.
> > >
> > > Thanks
>
> ------------------------------------
>
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