Adjust Dense Vector Unit Vector Epsilon

[Mikep86]

Change dense vector unit vector epsilon to 1e-3. This is required because Cohere sometimes generates unit vectors with magnitude slightly outside our current epsilon. For example, we have observed Cohere unit vectors with magnitude 1.0001829.

[elasticsearchmachine]

Pinging @elastic/es-search (Team:Search)

[Mikep86]

What tests, if any, should we add for this change?

[carlosdelest]

What tests, if any, should we add for this change?

Would the Cohere vectors you found be good candidates for a test?

[Mikep86]

@elasticsearchmachine run elasticsearch-ci/part-3

[Mikep86]

@elasticsearchmachine run elasticsearch-ci/8.15.0 / bwc-snapshots

[Mikep86]

@elasticsearchmachine run "elasticsearch-ci/8.15.0 / bwc-snapshots"

[Mikep86]

@elasticsearchmachine run elasticsearch-ci/bwc-snapshots

[Mikep86]

@elasticsearchmachine run elasticsearch-ci

[Mikep86]

Would the Cohere vectors you found be good candidates for a test?

Not really. While they are an example of unit vectors that violate the current epsilon, there is no way to know whether they are representative of the global maximum magnitude variance that Cohere will return.

We could add a test demonstrating that some set of hard-coded vectors are within the adjusted epsilon, but given that both the vectors and the epsilon are (or would be) hard-coded, I don't know what value that adds.

I will merge without tests and we can add some in a follow-up PR if we want to revisit.