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Single precision floating point arithmetic is a known problem with
Metastock - a search thru archives should turn up previous relevant
discussions - last time was to do with date arithmetic if I remember
correctly.
Given that the MS Formula Language is not a true programming language with
control of variable types and type coercion/conversion etc. I think all you
can do is be aware of the problem and try and code formulas accordingly to
minimise problem using functions like prec(), int(), abs() etc. I believe
all numeric variables in Metastock are held as float so even when you code a
constant "2" (intending an integer constant) it is stored internally as
float.
Comparing two variables (i.e. floating point numbers)for equality can often
not give the expected true result (due to minor difference in low order
digits). The usual workaround is to instead test the difference between the
numbers for a very small value.
John
----- Original Message -----
From: "Genevieve, Louisa, Herve" <genher@xxxxxxxxxxxxx>
To: <metastock@xxxxxxxxxxxxx>
Sent: Tuesday, October 02, 2001 7:58 AM
Subject: RE: Calculation error in MS
> When I replicated the experiment I created a security with, as closes 1.47
> and 1.5 as Orea's. I, then, read David's reply, and thought if I enter
1.47
> why would MS store it (internally) as 1.47000...1?David, do you mean that
> at a basic binary level , MS can not store a number with infinite 0's, as
> 1.4700000000......and therefore has to store it as 1.47000.....1? But if
it
> was the case , then, could the result of a calculation EVER be equal to a
> fix number? In the case of Orea's problem the result of the calculation IS
2
> ( and not 2.000001), if it get strored as 2.000001 then this could never
be
> equal to 2?? right??? In wich case, any formula of the type if( the
resultat
> of a calculation=a fix number(2 for instance), Do someting, Do somethin
> else) will NEVER work! I am very confused.......Anyone has more thoughts
on
> the subject?
>
> Herve
>
> -----Original Message-----
> From: owner-metastock@xxxxxxxxxxxxx
[mailto:owner-metastock@xxxxxxxxxxxxx]On
> Behalf Of David Jennings
> Sent: Monday, 1 October 2001 4:42 AM
> To: metastock@xxxxxxxxxxxxx
> Subject: Re: Calculation error in MS
>
>
> I can't say i have tried to replicate your results, but it doesn't seem
> unexpected. It relates to the precision of data held in MetaStock. I'm
sure
> there are similar experiences in the archives. Take heart, MetaStock is
not
> alone in this. Other trading programs suffer from the same problem e.g.
> TradeStation and also databases e.g. Microsoft SQL server. If you look at
> the internal representation it may well be 2.000000001 because 1.47 was
held
> as 1.4700000001 say. This should not be seen as a limitation, but as
> something to be aware of, especially if you are subtracting a small
number
> from a large number or calculating over long time periods. I would urge
you
> to look at the absolute tolerance, rather than the number itself. There
are
> a number of techniques around to get over such
> ----- Original Message -----
> From: "SR" <raftsp@xxxxxxxxx>
> To: <metastock@xxxxxxxxxxxxxxxxxx>
> Sent: Monday, October 01, 2001 10:26 AM
> Subject: RE: Calculation error in MS
>
>
> > Hello dear friends
> >
> > Today I noticed the following very strange error, while back-testing
with
> > Metastock 6.52 for windows:
> >
> > Previous bar's close = 1.5
> > This bar's close = 1.47
> >
> > All the calculations made (manually or electronically ) will agree that
> the
> > percentage of this change is -2
> > I made an indicator for calculating the change in MS itself, which also
> > agrees with this percentage:
> >
> > ( C - Ref(C, -1) ) * 100 / Ref(C, -1)
> >
> > The above returns -2 allright.
> >
> > So far so good.
> > But the strange thing is, that when I tried to verify this percentage
with
> > binary or ternary indicators, they did NOT recognize the change -2% as
> true!
> > In fact, they consider the result as >2% !
> > Here is a ternary indicator that I used for verification :
> >
> > perc:= ( C - Ref(C, -1) ) * 100 / Ref(C, -1);
> > If(perc > -2, 1,
> > If(perc < -2, -1, 0))
> >
> > The result returned in the above case was NOT zero (0) as it should be,
> but
> > one (1) which means that the change is represented by a number larger
> > than -2
> >
> > Has anybody else experienced such a thing? Do I have a virus in my
> computer?
> > A math terrorist maybe? Has my MS crashed quietly?
> > Can someone repeat the above experiment and tell me the results please?
> >
> > Thanks
> > Orea
> >
> >
> >
>
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