[R] Convert back to lower triangular matrix

[David Winsemius]

On Nov 15, 2011, at 5:38 PM, Juliet Ndukum wrote:

> Given a vector;> ab = seq(0.5,1, by=0.1)

> > ab[1] 0.5 0.6 0.7 0.8 0.9 1.0
> The euclidean distance between the vector elements is given by the  
> lower triangular matrix

> > dd1 = dist(ab,"euclidean")

> > dd1    1   2   3   4   5

> 2 0.1
> 3 0.2 0.1
> 4 0.3 0.2 0.1
> 5 0.4 0.3 0.2 0.1
> 6 0.5 0.4 0.3 0.2 0.1
> Convert the lower triangular matrix to a full matrix

> > ddm = as.matrix(dd1)

> > ddm    1   2   3   4   5   61 0.0 0.1 0.2 0.3 0.4 0.52 0.1 0.0 0.1  
> 0.2 0.3 0.43 0.2 0.1 0.0 0.1 0.2 0.34 0.3 0.2 0.1 0.0 0.1 0.25 0.4  
> 0.3 0.2 0.1 0.0 0.16 0.5 0.4 0.3 0.2 0.1 0.0
> I would be grateful if someone could provide me with a code to  
> convert ddm to the lower triangular matrix as before i.e. dd1

Surely this would be the logical inverse

dd1.b <- as.dist(ddm)

-- 
David Winsemius, MD
West Hartford, CT