Find a 2-D plane in 4-D space
Generate 1000 data points in a unit disk on a 2-D plane.
Generate 1000 data points in a ring outside the unit disk
Append the two sets of data together in a 2-D plane; this gives the original x and y variables
Suppose we are given four variables x1,x2,x3,x4, which are just some linear combinations of the original x and y variables
We shall use pca-model to find the original 2-D plane.