add neighbor calculation for angular_v1

virtdata-lib-basics/src/main/java/io/nosqlbench/virtdata/library/basics/shared/vectors/dnn/DNN_angular1_neighbors.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright (c) 2023 nosqlbench
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.nosqlbench.virtdata.library.basics.shared.vectors.dnn;
+
+import io.nosqlbench.virtdata.api.annotations.Categories;
+import io.nosqlbench.virtdata.api.annotations.Category;
+import io.nosqlbench.virtdata.api.annotations.ThreadSafeMapper;
+
+import java.util.function.IntFunction;
+
+/**
+ * Compute the indices of the neighbors of a given v using DNN mapping.
+ * To avoid ambiguity on equidistant neighbors, odd neighborhood sizes are preferred.
+ */
+@ThreadSafeMapper
+@Categories(Category.experimental)
+public class DNN_angular1_neighbors implements IntFunction<int[]> {
+
+    private final int N;
+    private final int k;
+    private final int modulus;
+
+    /**
+     * @param k
+     *     The size of neighborhood
+     * @param N
+     *     The number of total vectors, necessary for boundary conditions of defined vector
+     * @param module
+     *     The modulus used during training of angular1 data; this corresponds to how periodically we cycle back
+     *     to vectors with the same angle (hence have angular distance zero between them)
+     */
+    public DNN_angular1_neighbors(int k, int N, int modulus) {
+        if (modulus <= 0) {
+            throw new IllegalArgumentException(
+                String.format(
+                    "Invalid parameters: modulus=%d. modulus is required to be positive.",
+                    modulus
+                )
+            );
+        }
+        if (k * modulus > N) {
+            throw new IllegalArgumentException(
+                String.format(
+                    "Invalid parameters: N=%d, k=%d, modulus=%d. Vectors in a cluster = N / modulus >= k.",
+                    N, k, modulus
+                )
+            );
+        }
+        this.N = N;
+        this.k = k;
+        this.modulus = modulus;
+    }
+
+    /**
+     * @param value
+     *     the function argument, or the index of the query vector for the DNN addressing scheme
+     * @return A ranked neighborhood of vector indices, using the DNN addressing scheme
+     */
+    @Override
+    public int[] apply(int value) {
+        // we created modulus clusters of our N vectors, of size N/modulus or N/modulus + 1
+        // (the latter case when modulus does not evenly divide N, and we get remainder)
+        int div = N / modulus;
+        int mod = N % modulus;
+        int cycleResidueClass = value % modulus;
+        // handle case of extra neighbor in the same cluster
+        if (cycleResidueClass < mod) {
+            div += 1;
+        }
+        int[] indices = new int[div];
+        int currIdx = cycleResidueClass;
+        for (int i = 0; i < div; i++) {
+            indices[i] = currIdx;
+            currIdx += modulus;
+        }
+        return indices;
+    }
+}