code: public DoublesSketch downSample(final DoublesSketch srcSketch, final int smallerK,
                                    final WritableMemory dstMem) {
      return downSampleInternal(srcSketch, smallerK, dstMem);
    }
docs: From an source sketch, create a new sketch that must have a smaller value of K.
  The original sketch is not modified.
  
  @param srcSketch the sourcing sketch
  @param smallerK the new sketch's value of K that must be smaller than this value of K.
  It is required that this.getK() = smallerK * 2^(nonnegative integer).
  @param dstMem the destination Memory.  It must not overlap the Memory of this sketch.
  If null, a heap sketch will be returned, otherwise it will be off-heap.
  
  @return the new sketch.