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Fixed KNN search formulas (#1447)
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Signed-off-by: Fanit Kolchina <[email protected]>

Signed-off-by: Fanit Kolchina <[email protected]>
(cherry picked from commit 2c74943)
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kolchfa-aws authored and github-actions[bot] committed Oct 5, 2022
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32 changes: 16 additions & 16 deletions _search-plugins/knn/approximate-knn.md
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Expand Up @@ -279,39 +279,39 @@ GET my-knn-index-1/_search
A space corresponds to the function used to measure the distance between two points in order to determine the k-nearest neighbors. From the k-NN perspective, a lower score equates to a closer and better result. This is the opposite of how OpenSearch scores results, where a greater score equates to a better result. To convert distances to OpenSearch scores, we take 1 / (1 + distance). The k-NN plugin the spaces the plugin supports are below. Not every method supports each of these spaces. Be sure to check out [the method documentation]({{site.url}}{{site.baseurl}}/search-plugins/knn/knn-index#method-definitions) to make sure the space you are interested in is supported.

<table>
<thead style="text-align: left">
<thead style="text-align: center">
<tr>
<th>spaceType</th>
<th>Distance Function</th>
<th>Distance Function (d)</th>
<th>OpenSearch Score</th>
</tr>
</thead>
<tr>
<td>l2</td>
<td>\[ Distance(X, Y) = \sum_{i=1}^n (X_i - Y_i)^2 \]</td>
<td>1 / (1 + Distance Function)</td>
<td>l1</td>
<td>\[ d(\mathbf{x}, \mathbf{y}) = \sum_{i=1}^n |x_i - y_i| \]</td>
<td>\[ score = {1 \over 1 + d } \]</td>
</tr>
<tr>
<td>l1</td>
<td>\[ Distance(X, Y) = \sum_{i=1}^n (X_i - Y_i) \]</td>
<td>1 / (1 + Distance Function)</td>
<td>l2</td>
<td>\[ d(\mathbf{x}, \mathbf{y}) = \sum_{i=1}^n (x_i - y_i)^2 \]</td>
<td>\[ score = {1 \over 1 + d } \]</td>
</tr>
<tr>
<td>linf</td>
<td>\[ Distance(X, Y) = Max(X_i - Y_i) \]</td>
<td>1 / (1 + Distance Function)</td>
<td>\[ d(\mathbf{x}, \mathbf{y}) = max(|x_i - y_i|) \]</td>
<td>\[ score = {1 \over 1 + d } \]</td>
</tr>
<tr>
<td>cosinesimil</td>
<td>\[ 1 - {A &middot; B \over \|A\| &middot; \|B\|} = 1 -
{\sum_{i=1}^n (A_i &middot; B_i) \over \sqrt{\sum_{i=1}^n A_i^2} &middot; \sqrt{\sum_{i=1}^n B_i^2}}\]
where \(\|A\|\) and \(\|B\|\) represent normalized vectors.</td>
<td>nmslib and faiss:<br>1 / (1 + Distance Function)<br>Lucene:<br>(1 + Distance Function) / 2</td>
<td>\[ d(\mathbf{x}, \mathbf{y}) = 1 - cos { \theta } = 1 - {\mathbf{x} &middot; \mathbf{y} \over \|\mathbf{x}\| &middot; \|\mathbf{y}\|}\]\[ = 1 -
{\sum_{i=1}^n x_i y_i \over \sqrt{\sum_{i=1}^n x_i^2} &middot; \sqrt{\sum_{i=1}^n y_i^2}}\]
where \(\|\mathbf{x}\|\) and \(\|\mathbf{y}\|\) represent normalized vectors.</td>
<td><b>nmslib</b> and <b>faiss:</b>\[ score = {1 \over 1 + d } \]<br><b>Lucene:</b>\[ score = {1 + d \over 2}\]</td>
</tr>
<tr>
<td>innerproduct (not supported for Lucene)</td>
<td>\[ Distance(X, Y) = - {A &middot; B} \]</td>
<td>if Distance Function is > or = 0, use 1 / (1 + Distance Function). Otherwise, -Distance Function + 1</td>
<td>\[ d(\mathbf{x}, \mathbf{y}) = - {\mathbf{x} &middot; \mathbf{y}} = - \sum_{i=1}^n x_i y_i \]</td>
<td>\[ \text{If} d \ge 0, \] \[score = {1 \over 1 + d }\] \[\text{If} d < 0, score = &minus;d + 1\]</td>
</tr>
</table>

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38 changes: 19 additions & 19 deletions _search-plugins/knn/knn-score-script.md
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Expand Up @@ -282,44 +282,44 @@ GET my-long-index/_search
A space corresponds to the function used to measure the distance between two points in order to determine the k-nearest neighbors. From the k-NN perspective, a lower score equates to a closer and better result. This is the opposite of how OpenSearch scores results, where a greater score equates to a better result. The following table illustrates how OpenSearch converts spaces to scores:

<table>
<thead style="text-align: left">
<thead style="text-align: center">
<tr>
<th>spaceType</th>
<th>Distance Function</th>
<th>Distance Function (d)</th>
<th>OpenSearch Score</th>
</tr>
</thead>
<tr>
<td>l2</td>
<td>\[ Distance(X, Y) = \sum_{i=1}^n (X_i - Y_i)^2 \]</td>
<td>1 / (1 + Distance Function)</td>
<td>l1</td>
<td>\[ d(\mathbf{x}, \mathbf{y}) = \sum_{i=1}^n |x_i - y_i| \]</td>
<td>\[ score = {1 \over 1 + d } \]</td>
</tr>
<tr>
<td>l1</td>
<td>\[ Distance(X, Y) = \sum_{i=1}^n (X_i - Y_i) \]</td>
<td>1 / (1 + Distance Function)</td>
<td>l2</td>
<td>\[ d(\mathbf{x}, \mathbf{y}) = \sum_{i=1}^n (x_i - y_i)^2 \]</td>
<td>\[ score = {1 \over 1 + d } \]</td>
</tr>
<tr>
<td>linf</td>
<td>\[ Distance(X, Y) = Max(X_i - Y_i) \]</td>
<td>1 / (1 + Distance Function)</td>
<td>\[ d(\mathbf{x}, \mathbf{y}) = max(|x_i - y_i|) \]</td>
<td>\[ score = {1 \over 1 + d } \]</td>
</tr>
<tr>
<td>cosinesimil</td>
<td>\[ {A &middot; B \over \|A\| &middot; \|B\|} =
{\sum_{i=1}^n (A_i &middot; B_i) \over \sqrt{\sum_{i=1}^n A_i^2} &middot; \sqrt{\sum_{i=1}^n B_i^2}}\]
where \(\|A\|\) and \(\|B\|\) represent normalized vectors.</td>
<td>1 + Distance Function</td>
<td>\[ d(\mathbf{x}, \mathbf{y}) = cos \theta = {\mathbf{x} &middot; \mathbf{y} \over \|\mathbf{x}\| &middot; \|\mathbf{y}\|}\]\[ =
{\sum_{i=1}^n x_i y_i \over \sqrt{\sum_{i=1}^n x_i^2} &middot; \sqrt{\sum_{i=1}^n y_i^2}}\]
where \(\|\mathbf{x}\|\) and \(\|\mathbf{y}\|\) represent normalized vectors.</td>
<td>\[ score = 1 + d \]</td>
</tr>
<tr>
<td>innerproduct</td>
<td>\[ Distance(X, Y) = \sum_{i=1}^n X_iY_i \]</td>
<td>1 / (1 + Distance Function)</td>
<td>innerproduct (not supported for Lucene)</td>
<td>\[ d(\mathbf{x}, \mathbf{y}) = - {\mathbf{x} &middot; \mathbf{y}} = - \sum_{i=1}^n x_i y_i \]</td>
<td>\[ \text{If} d \ge 0, \] \[score = {1 \over 1 + d }\] \[\text{If} d < 0, score = &minus;d + 1\]</td>
</tr>
<tr>
<td>hammingbit</td>
<td style="text-align:center">Distance = countSetBits(X \(\oplus\) Y)</td>
<td> 1 / (1 + Distance Function)</td>
<td>\[ d(\mathbf{x}, \mathbf{y}) = \text{countSetBits}(\mathbf{x} \oplus \mathbf{y})\]</td>
<td>\[ score = {1 \over 1 + d } \]</td>
</tr>
</table>

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