cluster (version 2.1.8)

lower.to.upper.tri.inds: Permute Indices for Triangular Matrices

Description

Compute index vectors for extracting or reordering of lower or upper triangular matrices that are stored as contiguous vectors.

Usage

lower.to.upper.tri.inds(n)
upper.to.lower.tri.inds(n)

Value

integer vector containing a permutation of 1:N where

\(N = n(n-1)/2\).

Arguments

n

integer larger than 1.

See Also

upper.tri, lower.tri with a related purpose.

Examples

m5 <- matrix(NA,5,5)
m <- m5; m[lower.tri(m)] <- upper.to.lower.tri.inds(5); m
m <- m5; m[upper.tri(m)] <- lower.to.upper.tri.inds(5); m

stopifnot(lower.to.upper.tri.inds(2) == 1,
          lower.to.upper.tri.inds(3) == 1:3,
          upper.to.lower.tri.inds(3) == 1:3,
     sort(upper.to.lower.tri.inds(5)) == 1:10,
     sort(lower.to.upper.tri.inds(6)) == 1:15)