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> >Can someone tell me if its possible to create an indicator
> >that is based on daily data but is effectively plotting
> >a weekly indicator? Such as plotting a 10 period RSI for example
> >but using today, 5 days ago, 10 days ago..etc...
>
> What you describe is easy. You just load up the built in function,
> modify it so that every occurence of Length is 5*Length, and save
> it under another name. In any loop, the step increment should be
> multiplied by 5 also.
That will produce a similar result, and possibly close enough for
what you need, but it's *NOT* going to produce the same results.
RSI is a little complicated, so let's look at a simpler function,
like xaverage. If you run xaverage on Length weekly bars, you'll
sample Length close values, one every 5 days. The closes on Monday
through Thursday have ABSOLUTELY NO EFFECT on the resulting xaverage
value. ONLY the Friday close is used in the calculation.
Now if you use daily data and calculate a 5*Length-long xaverage,
you're including Mon-Thur closes in your calculation. You can see
that this is not going to produce the same results. Similar, maybe,
but not the same. The most obvious difference is that the 5*Length
xaverage changes gradually on every bar, whereas the weekly xaverage
makes bigger jumps on every weekly bar.
> What you probably WANT is harder, if you want the weekly bars to
> correspond to the range monday-friday all the time. In that case
> you would have to maintain your own array of weekly bars, and have
> your various functions written especially for them.
It's actually possible to do it much simpler than that, at least for
some functions. If you can call the function only on Friday closes,
you'll get the same results as you'd get on a weekly chart. The
trick is to use a **Simple** function instead of a **Series**
function.
Series functions are implicitly called on EVERY bar, whether you call
them explicitly or not. It's strange, but it's part of the
definition of Easy Language. Simple functions, however, are called
only when you actually explicitly call them.
If you do something like this:
if DayOfWeek(Date) = 5 then RSIval = RSI(Close, Length);
...then it's NOT just calling RSI on Fridays, but on every bar --
because RSI is defined as a Series function.
If you write your own function that doesn't require access to
previous bar values -- which requires a Series function -- then you
can declare it to be a Simple function. Then, when you call it on
Fridays, it is really only called on Fridays, and you'll get exactly
the same results as if you called it on every bar of a weekly chart.
Unfortunately RSI *does* require access into past history.
Fortunately it really only needs that for its initialization. If you
look at the definition of RSI, you'll see that after CurrentBar = 1
it only refers to the previous bar's value of Price, UpAvg, and
DownAvg. That's easily handled just by using the value that's
carried forward into each new bar; at the start of the bar, the
variables all hold the value they had in the previous bar, and you
don't need to access the historic values (e.g. UpAvg[1]) at all.
So it would be a matter of rewriting RSI to initialize itself without
historic values, and then don't use the [BarsBack] history access in
the function. Declare the function to be Simple, call it only on
Friday closes, and you'll get the identical results that you would
have gotten in a weekly chart.
Or maybe using 5*Length is "close enough" for your needs, and simpler.
:-)
Gary
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