library(mvtnorm)
library(MASS)
set.seed(09101964)
s   <- matrix(c(1, 0.8, 0.8, 1), nr=2)
x   <- rmvnorm(20, sigma=s)
x   <- sweep(x, 2, apply(x, 2, mean))
d   <- sqrt(x[,1]*x[,1]+x[,2]*x[,2])
pos <- which.max(d)
d   <- max(d)
pca <- princomp(x)
eqscplot(x, axes=F)
mx  <- apply(x, 2, mean)
points(x=mx[1], y=mx[2], pch=19, cex=2)
psi <- min(pca$scores[,1])
psa <- max(pca$scores[,1])
p1  <- pca$loadings[,1]*psi
p2  <- pca$loadings[,1]*psa
pc1 <- matrix(c(p1,p2), nc=2, byrow=T)
lines(pc1, col="black", lwd=2)
if (-psi>psa) p3 <- p1 else p3 <- p2
lines(x=c(mx[1],p3[1], x[pos,1], mx[1]),y=c(mx[2], p3[2], x[pos,2], mx[2]), col="red", lwd=1)

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