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https://issues.apache.org/jira/browse/MAHOUT-267?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jake Mannix reassigned MAHOUT-267:
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Assignee: Jake Mannix
> Vector.norm(x) uses incorrect formula for both x == POSITIVE_INFINITY and x
> == 1
> --------------------------------------------------------------------------------
>
> Key: MAHOUT-267
> URL: https://issues.apache.org/jira/browse/MAHOUT-267
> Project: Mahout
> Issue Type: Bug
> Components: Math
> Affects Versions: 0.1, 0.2
> Environment: all
> Reporter: Jake Mannix
> Assignee: Jake Mannix
> Priority: Minor
> Fix For: 0.3
>
>
> Ugh. This is the second time I've had to fix the definition of an L_p norm
> in an Apache project.
> {code}
> @Override
> public double norm(double power) {
> if (power < 0.0) {
> throw new IllegalArgumentException("Power must be >= 0");
> }
> // we can special case certain powers
> if (Double.isInfinite(power)) {
> return maxValue();
> } else if (power == 2.0) {
> return Math.sqrt(dot(this));
> } else if (power == 1.0) {
> return zSum();
> } else if (power == 0.0) {
> ...
> }
> {code}
> Spot the errors? Hint: both maxValue() and zSum() can return negative
> values, which is a no-no for norms unless we're going to do Relativity and
> have Lorentzian metrics allowed in Mahout:
> * maxValue() returns the maximum (meaning: closest to POSITIVE_INFINITY)
> value, which means large negative numbers aren't noticed and factored in.
> * zSum() adds all the values - not their absolute values.
> I'll check in a fix with some of my other code, but I wanted this tracked, as
> apparently the norm(double) method is so often used that this was never
> noticed in unit tests OR by users (the fact that nobody's ever noticed this
> makes me log this as a "minor" bug). :(
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