code: public static Generator<List<List<Long>>> iterateOverSparse(INDArrayIndex... indexes) {
          Generator<List<List<Long>>> gen = Itertools.product(new SparseSpecifiedIndexesGenerator(indexes));
          return gen;
      }
docs: Iterate over a cross product of the
  coordinates
  @param indexes the coordinates to iterate over.
  Each element of the array should be of opType {@link SpecifiedIndex}
  otherwise it will end up throwing an exception
  @return the generator for iterating over all the combinations of the specified indexes.