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anna-charlotte merged 2 commits into from
Apr 28, 2023
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docs: change cosine similarity to distance for hnswlib doc index #1476

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docs: change cosine similarity to distance for hnswlib doc index
Apr 28, 2023
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fix: apply joans suggestion from code review
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23 changes: 13 additions & 10 deletions docs/user_guide/storing/index_hnswlib.md
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Expand Up @@ -123,16 +123,19 @@ In the example above you can see how to configure two different vector fields, w

In this way, you can pass [all options that Hnswlib supports](https://github.com/nmslib/hnswlib#api-description):

| Keyword | Description | Default |
|-------------------|--------------------------------------------------------------------------------------------------------------------------------|---------|
| `max_elements` | Maximum number of vector that can be stored | 1024 |
| `space` | Vector space (similarity metric) the index operates in. Supports 'l2', 'ip', and 'cosine' | 'l2' |
| `index` | Whether or not an index should be built for this field. | True |
| `ef_construction` | defines a construction time/accuracy trade-off | 200 |
| `ef` | parameter controlling query time/accuracy trade-off | 10 |
| `M` | parameter that defines the maximum number of outgoing connections in the graph | 16 |
| `allow_replace_deleted` | enables replacing of deleted elements with new added ones | True |
| `num_threads` | sets the number of cpu threads to use | 1 |
| Keyword | Description | Default |
|-------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------|
| `max_elements` | Maximum number of vector that can be stored | 1024 |
| `space` | Vector space (distance metric) the index operates in. Supports 'l2', 'ip', and 'cosine'. <br/><span style="color:black">**Note:** In contrast to the other backends, for HnswDocumentIndex `'cosine'` refers to **cosine distance**, not cosine similarity. To transform one to the other, you can use: `cos_sim = 1 - cos_dist`. For more details see [here](https://en.wikipedia.org/wiki/Cosine_similarity#Cosine_Distance)</span>. | 'l2' |
| `index` | Whether or not an index should be built for this field. | True |
| `ef_construction` | defines a construction time/accuracy trade-off | 200 |
| `ef` | parameter controlling query time/accuracy trade-off | 10 |
| `M` | parameter that defines the maximum number of outgoing connections in the graph | 16 |
| `allow_replace_deleted` | enables replacing of deleted elements with new added ones | True |
| `num_threads` | sets the number of cpu threads to use | 1 |

!!! note
In HnswLibDocIndex `space='cosine'` refers to cosine distance, not to cosine similarity, as it does for the other backends.

You can find more details on the parameters [here](https://github.com/nmslib/hnswlib/blob/master/ALGO_PARAMS.md).

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