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[amibroker] Lesson Learned NZ Function.

To: <amibroker@xxxxxxxxxxxxxxx>
Subject: [amibroker] Lesson Learned NZ Function.
From: "David Fitch" <davidfitch@xxxxxxxxxxx>
Date: Wed, 11 Jan 2006 09:03:43 -0800

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I'd like to pass along a lesson this nonprogrammer learned. Read the directions. I've been using a Chaiken function to make a surrogate for an uptrend instead of advance decline line. Werner Ganz thought up the idea and it seemed to work nicely. Here's code;

chk = Nz(Sum(((( C-L )-( H-C )) / (H-L))*V, 21) / Sum(V, 21));

Composites were made to show when this was positive on a list of tickers and plotted as a % of total tickers. Usually it centers around the 50% line + or - 15%. Lately it read 95%+. But it seemed to work on an old version of AB.

Turned out it was the NZ function causing the problem. NZ keeps the formula from blowing up when H = L or just bad data. It returns 0.0 instead of nonsense. But the latest version of AB beta has been changed to speed things up.

From Marcin:

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Use:

SetOption("EveryBarNullCheck", True)

Indeed - the arrays where you have nulls in the middle are calculated differently in the latest betas.

In the readme file you can read:

SetOption("EveryBarNullCheck", True)- allows to turn on checking for Nulls in arithmetic operations on every bar in the array(by default it is OFF - i.e. AmiBroker checks for nulls that appear in the beginning of the array and in the end of the array and once non-null value is detected it assumes no further holes (nulls) in the middle). Turning "EveryBarNullCheck" to True allows to extend these checks to each and every bar which is the way 4.74.x and earlier versions worked.

Note however that turning it on gives huge performance penalty (arithmetic operations are performed even 4x slower when this option is ON, so don't use it unless you really have to).