兄弟过奖了，我是百思不得其解，在你的启发下才有所突破的。
但是还有未解的，左下横纵坐标明白了，但右边和上边仍有两个坐标轴，我还没弄明白。

值得好好学习呀

A biplot is constructed by using the singular value decomposition (SVD) to obtain a low-rank approximation to a transformed version of the data matrix X, whose n rows are the samples (also called the cases, or objects), and whose p columns are the variables. The transformed data matrix Y is obtained from the original matrix X by centering and optionally standardizing the columns (the variables). Using the SVD, we can write Y = ∑k=1,...pdkukvkT;, where the uk are n-dimensional column vectors, the vk are p-dimensional column vectors, and the dk are a non-increasing sequence of non-negative scalars. The biplot is formed from two scatterplots that share a common set of axes and have a between-set scalar product interpretation. The first scatterplot is formed from the points (d1αu1i,  d2αu2i), for i = 1,...,n. The second plot is formed from the points (d11-αv1j, d21-αv2j), for j = 1,...,p. This is the biplot formed by the dominant two terms of the SVD, which can then be represented in a two-dimensional display. Typical choices of α are 1 (to give a distance interpretation to the row display) and 0 (to give a distance interpretation to the column display), and in some rare cases α=1/2 to obtain a symmetrically scaled biplot (which gives no distance interpretation to the rows or the columns, but only the scalar product interpretation). The set of points depicting the variables can be drawn as arrows from the origin to reinforce the idea that they represent biplot axes onto which the samples can be projected to approximate the original data.
按照上面的试了一下，跟这个不一样，你再琢磨一下

Read more: http://www.answers.com/topic/biplot#ixzz1oOSmXsFe

多谢小王子！

楼主你好！我看到了你提的这个问题，想请教你一下：图中的x1-x4的方向、长度、斜率都代表什么呀？谢谢解释：）