Nonlinear biplots
将经典双标图推广到任意欧几里得可嵌入距离，用非线性轨迹表示变量，帮助解释排序图中的样本点，适用于多种度量或非度量缩放及结构化多元样本。
The classical biplot (Gabriel, 1971) of a multivariate sample X of n units by p variables is generalized for any Euclidean imbeddable metric dij. Sample-units are represented in the usual way by points in an ordination, most conveniently using principal coordinates. Variables are represented by a set of p concurrent nonlinear trajectories whose lengths and dispositions relative to the sample points aid interpretation. When dij2 is defined to have independent contributions from each variable, the centroid of any p points, one on each trajectory, may be used to interpolate and interpret sample points in the ordination. The basic idea may be exploited further for use with any form of metric or nonmetric scaling and for structured multivariate samples.