INF, NAN, and Null

Revision as of 22:01, 13 January 2015 by Psanford (Talk | contribs) (Psanford moved page INF, NAN, Null, and Undefined to INF, NAN, and Null: Remove "Undefined" from the title)


These are special values that Analytica returns in special conditions:

Inf means infinity -- e.g., 1/0 -- or a real number larger than can be represented -- e.g. 1E307 * 100, because the maximum number it can handle is 1.796E308.
-Inf rmeans negative infinity -- e.g., -1/0 -- or a number smaller than can be represented
NAN means "Not A Number", where the result is numeric, but not a real number or infinity -- e.g., Sqrt(-1) or 0/0
Null means that there is no such value. Slice, Subscript, SubIndex, or MdTable return Null, for example, when trying to Slice out the nth slice over an Index with less than n values.

Computations with special values

Analytica follows ANSI (Association of National Standards Institutes) standards for computing with these special values, where applicable.

1/Inf → 0
1/(-Inf) → 0
Inf + Inf → Inf
Inf - Inf → NAN

When NULL appears in scalar operations, it generally produces a warning and evaluates to NULL, for example:

10 + NULL → NULL
NULL - 10 → NULL
1 AND NULL → NULL

When NULL appears in an array operation, the result should be ignored. The common array reduction functions in Analytica 4.1 tend to support this as of release 4.1, but not prior to that, and not all array function support this. These examples demonstrate (assume A is indexed by I as indicated).

I: 1 2 3 4 5
A: 8 NULL 4 NULL 0
Sum(A,I) → 12
Average(A,I) → 4
Join(A,I,',') → "8,4,0"

In Analytica 4.1, these array functions ignore Null: Sum, Min, Max, ArgMin, ArgMax, Product, Average, JoinText, Irr, Npv. Also Regression ignores data points which have Y=Null.

Array functions Sum, Min and Max also accept an optional parameter IgnoreNaN to ignore NaN values (otherwise they tend to be propagated).

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