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Tomasz,
thank you for details.
I understand that you follow some convention NULL+X=NULL.
I am not sure it reflects the common addition logic.
Nz solves the alternative.
Some clarification of the use of the above convention would not be a
bad idea for the AFL reference.
Dimitris Tsokakis
--- In amibroker@xxxxxxxxxxxxxxx, "Tomasz Janeczko" <amibroker@xxxx>
wrote:
> Dimitris,
>
> The {empty} ( or Null) in AmiBroker works as NULL in the databases.
>
> When any part of arithmetic expression is NULL the entire
expression becomes NULL.
> Null (empty) means in fact "UNKNOWN"
> If you add 2 + UNKNOWN the result is still UNKNOWN.
>
> For example for the first 20 bars the value of MA( Close, 20 ) is
UNKNOWN (empty).
>
> As for DB examples see:
> http://msdn.microsoft.com/library/default.asp?url=/library/en-
us/off2000/html/acconCalcControlExpUseArithmeticOperators.asp
>
>
> AB 4.29.8 features new function Nz
> http://www.amibroker.com/guide/afl/afl_view.php?name=NZ
>
> that allows to easily convert Null (empty) to zero:
>
> Nz( Foreign("RATL","O") ) + Nz( Foreign("CSCO","O") )
>
> Best regards,
> Tomasz Janeczko
> amibroker.com
> ----- Original Message -----
> From: Dimitris Tsokakis
> To: amibroker@xxxxxxxxxxxxxxx
> Sent: Thursday, March 06, 2003 11:37 AM
> Subject: [amibroker] Some strange addition rules
>
>
> I noticed that
> {empty}+X={empty}
> X+{empty}={empty}
> One should expect {empty}+X=X.
> Consequently, special care should be taken with similar additions
[or subtractions, multiplications, divisions]
> If you try to add Foreign("RATL","O")+Foreign("CSCO","O") and the
RATL data is missing for a certain bar, the result would be {empty}
> instead of the expected Foreign("CSCO","O")
> Dimitris Tsokakis
>
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