# [R] stats/debugging question hotelling t-sq

From: <toby909_at_gmail.com>
Date: Sun, 16 Mar 2008 04:09:00 -0700

Hi

help appreciated.

```x = as.matrix(read.table("http://www.niehs.nih.gov/research/atniehs/core/microarrays/docs/heinloth.txt",1))
x = t(x)    #now rows are subjects, cols are genes
x = x[order(rownames(x)),]    #order by treatment group oxygen,
```
```y = x[26:45,1:10]
x = x[2:25,1:10]
p = ncol(x); p
```

nx = nrow(x); nx
ny = nrow(y); ny
n = nx+ny; n

# (t(x)-colMeans(x)) %*% t(t(x)-colMeans(x))

T2 = nx*ny/n * t(colMeans(x)-colMeans(y)) %*% solve( ( (nx-1)*cov(x)+(ny-1)*cov(y) )/( n-2 ) ) %*% (colMeans(x)-colMeans(y)); T2

library(ICSNP)
HotellingsT2(y,x)

http://en.wikipedia.org/wiki/Hotelling's_T-square_distribution

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