added serial cluster implementation (edge-wise), should ne however node-wise

torch_cluster/src/cpu.c

@@ -2,5 +2,20 @@
 
 #define cluster_(NAME) TH_CONCAT_4(cluster_, NAME, _, Real)
 
+void cluster_serial(THLongTensor *output, THLongTensor *row, THLongTensor *col) {
+  int64_t *output_data = output->storage->data + output->storageOffset;
+  int64_t *row_data = row->storage->data + row->storageOffset;
+  int64_t *col_data = col->storage->data + col->storageOffset;
+  int64_t n, N = THLongTensor_nElement(output), r, c, value;
+  for (n = 0; n < N; n++) {
+    r = row_data[n]; c = col_data[c];
+    if (output_data[r] == -1 && output_data[c] == -1) {
+      value = r < c ? r : c;
+      output_data[r] = value;
+      output_data[c] = value;
+    }
+  }
+}
+
 #include "generic/cpu.c"
 #include "THGenerateAllTypes.h"

torch_cluster/src/cpu.h

@@ -5,3 +5,5 @@ void cluster_grid_Char  (int C, THLongTensor *output, THCharTensor   *position,
 void cluster_grid_Short (int C, THLongTensor *output, THShortTensor  *position, THShortTensor  *size, THLongTensor *count);
 void cluster_grid_Int   (int C, THLongTensor *output, THIntTensor    *position, THIntTensor    *size, THLongTensor *count);
 void cluster_grid_Long  (int C, THLongTensor *output, THLongTensor   *position, THLongTensor   *size, THLongTensor *count);
+
+void cluster_serial(THLongTensor *output, THLongTensor *row, THLongTensor *col);