David Pottinger Stephen Todd Iain Rodrigues Tom Mullin Anne Skeldon Phase portraits for parametrically excited pendula: An exercise in multidimensional data visualisation. 331-337 1992 16 Computers & Graphics 3 http://dx.doi.org/10.1016/0097-8493(92)90012-K db/journals/cg/cg16.html#PottingerTRMS92