Make the thresholds in TestLowCardinalityFiltering tighter (#559)

Reduce the number of vectors in TestLowCardinalityFiltering and adjust the thresholds to make them tighter

Author: marianotepper

jvector-tests/src/test/java/io/github/jbellis/jvector/graph/TestLowCardinalityFiltering.java

@@ -45,15 +45,19 @@
 
 @ThreadLeakScope(ThreadLeakScope.Scope.NONE)
 public class TestLowCardinalityFiltering extends LuceneTestCase {
+    /*
+    This test replicates https://github.com/jbellis/pwtest/tree/master natively in JVector.
+    It splits the vectors in two classes (with probability 0.5) and tests that the filtering works when the query belongs to one of them.
+     */
     @Test
     public void testLowCardinalityFiltering() throws IOException {
-        testLowCardinalityFiltering(32, 0.01f, 0.87f, false);
-        testLowCardinalityFiltering(32, 0.01f, 0.87f, true);
+            testLowCardinalityFiltering(32, 0.044f, 0.91f, false);
+            testLowCardinalityFiltering(32, 0.048f, 0.93f, true);
     }
     public void testLowCardinalityFiltering(int maxDegree, float visitedRatioThreshold, float recallThreshold, boolean addHierarchy) throws IOException {
         var R = getRandom();
 
-        int nVectors = 100_000;
+        int nVectors = 10_000;
         int nQueries = 100;
         int dimensions = 16;
         int topK = 10;