code: public CirculantGraph addRange(long offset, long length) {
  		Preconditions.checkArgument(offset >= MINIMUM_OFFSET,
  			"Range offset must be at least " + MINIMUM_OFFSET);
  		Preconditions.checkArgument(length <= vertexCount - offset,
  			"Range length must not be greater than the vertex count minus the range offset.");
  
  		offsetRanges.add(new OffsetRange(offset, length));
  
  		return this;
  	}
docs: Required configuration for each range of offsets in the graph.
  
  @param offset first offset appointing the vertices' position
  @param length number of contiguous offsets in range
  @return this