[GitHub] [lucene-solr] jtibshirani commented on a change in pull request #2047: LUCENE-9592: Use doubles in VectorUtil to maintain precision.

[GitBox <gi...@apache.org>]

jtibshirani commented on a change in pull request #2047:
URL: https://github.com/apache/lucene-solr/pull/2047#discussion_r524826537



##########
File path: lucene/core/src/java/org/apache/lucene/util/VectorUtil.java
##########
@@ -25,47 +25,22 @@
   private VectorUtil() {
   }
 
-  public static float dotProduct(float[] a, float[] b) {
-    float res = 0f;
-    /*
-     * If length of vector is larger than 8, we use unrolled dot product to accelerate the
-     * calculation.
-     */
-    int i;
-    for (i = 0; i < a.length % 8; i++) {
-      res += b[i] * a[i];
-    }
-    if (a.length < 8) {
-      return res;
-    }
-    float s0 = 0f;
-    float s1 = 0f;
-    float s2 = 0f;
-    float s3 = 0f;
-    float s4 = 0f;
-    float s5 = 0f;
-    float s6 = 0f;
-    float s7 = 0f;
-    for (; i + 7 < a.length; i += 8) {
-      s0 += b[i] * a[i];
-      s1 += b[i + 1] * a[i + 1];
-      s2 += b[i + 2] * a[i + 2];
-      s3 += b[i + 3] * a[i + 3];
-      s4 += b[i + 4] * a[i + 4];
-      s5 += b[i + 5] * a[i + 5];
-      s6 += b[i + 6] * a[i + 6];
-      s7 += b[i + 7] * a[i + 7];
+  public static double dotProduct(float[] a, float[] b) {

Review comment:
       Simply changing the test to use a larger epsilon sounds good to me. After thinking about this more, I'm not sure we want to optimize for the precision of these individual calculations. Many high-dimensional vectors are already an approximation to an original object, like a piece of text. And I've heard of practitioners choosing less precise representations (like bfloat16) for each vector element to save space, and still achieving acceptable results.




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