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GP,
Thanks for your detailed response here.
I'm not sure I can see why the solution suggested by Graham won't
work. Sorry if I'm being dense, but while you absolutely prove that,
temp = BarIndex() < 10;
varx = temp AND NOT Ref(temp,-1);
and
varx = BarIndex() < 10 AND NOT Ref(varx,-1);
are indeed not the same solution... it seems to me that the former
does actually get me what I want. And does so by evaluating temp
first. Again, I might be missing something here. I try and implement
that solution into my code and let you know if I get the desired result.
TIA
--- In amibroker@xxxxxxxxxxxxxxx, "gp_sydney" <gp.investment@xxx> wrote:
>
> Graham,
>
> That doesn't work either, in the general case, as varx is still not
> dependent on previous values of varx, only on previous values of your
> first "temp" statement.
>
> Consider the simpler case:
>
> temp = BarIndex() < 10;
> varx = temp AND NOT Ref(temp,-1);
>
> temp now has the first 10 bars set to one and all other bars set to
> zero. varx will have the first 11 bars set to zero, since Ref(temp,-1)
> is one (actually the first bar will probably be null) and then all
> subsequent bars will also be zero since temp is then zero.
> Consequently, varx would be completely zero, except perhaps for the
> first null.
>
> Assuming this did work as suggested, compare to:
>
> varx = BarIndex() < 10 AND NOT Ref(varx,-1);
>
> Actually if the first bar was null due to Ref(varx,-1) being null,
> then varx would end up completely full of nulls (a problem to be wary
> of with nulls in loops). But say the first bar ended up being zero
> (perhaps the nz function was used), then the second bar would be one,
> since BarIndex is less than 10 and Ref(varx,-1) refers to the first
> bar which we just said was zero. The third bar would be zero, since
> Ref(varx,-1) now refers to the second bar which we just set to one,
> and the fourth bar would be one again. This would continue up to the
> 10th bar, after which all bars would be zero due to the BarIndex term.
> The first 10 bars of varx alternating between one and zero make the
> result different to the first version.
>
> Regards,
> GP
>
>
> --- In amibroker@xxxxxxxxxxxxxxx, Graham <kavemanperth@> wrote:
> >
> > try this
> > temp = C<Ref(L,-6) AND vary<6;
> > varx = temp AND NOT Ref(temp ,-6);
> >
> > --
> > Cheers
> > Graham Kav
> > AFL Writing Service
> > http://www.aflwriting.com
> >
> >
> >
> >
> > 2008/9/18 gp_sydney <gp.investment@>:
> > > No, you can't do that as the right-hand expression is evaluated
on the
> > > whole array before anything is assigned to the left-hand variable.
> > > That means that "varx" is effectively constant during the expression
> > > evaluation for the whole array. It's essentially the same as:
> > >
> > > temp = IIf(C<Ref(L,-6) AND vary<6 AND NOT Ref(varx,-6),True,False);
> > > varx = temp;
> > >
> > > To do what you are suggesting would require a loop.
> > >
> > > Regards,
> > > GP
> > >
> > >
> > > --- In amibroker@xxxxxxxxxxxxxxx, "sidhartha70" <sidhartha70@>
wrote:
> > >>
> > >> Hi All,
> > >>
> > >> Is it possible to have recursive boolean expressions...? i.e. the
> true
> > >> or false of the current value of the array depends on whether a
> > >> previous value of the array is true or false.
> > >>
> > >> So for example,
> > >>
> > >> varx = IIf(C<Ref(L,-6) AND vary<6 AND NOT Ref(varx,-6),True,False);
> > >>
> > >> Would that work... or are recursive booleans like this not
allowed??
> > >>
> > >> TIA
> > >>
> >
>
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