vechMat: Vectorization and Expansion of Symmetric Matrices
In mixmeta: An Extended Mixed-Effects Framework for Meta-Analysis

Description Usage Arguments Value Author(s) See Also Examples

The function vechMat transforms a symmetric matrix in a vector containing its lower triangular elements, taken by column. The function xpndMat reverses this transformation.

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vechMat(mat, diag=TRUE)

xpndMat(vech)

`mat`	a square matrix.
`vech`	a vector.
`diag`	a logical switch indicating if the diagonal entries must be included.

A vector for vechMat, a symmetric matrix for xnpdMat.

Antonio Gasparrini <antonio.gasparrini@lshtm.ac.uk>

See functions vech and xpnd in package MCMCpack.

# GENERATE A POSITIVE-DEFINITE MATRIX, VECTORIZE IT AND THEN RE-EXPAND
(M <- crossprod(matrix(rnorm(9),3)))
(v <- vechMat(M))
xpndMat(v)

# EXTRACT VECTORIZED S, EXPAND TO A LIST, AND RE-VECTORIZE
(S <- as.matrix(berkey98[5:7]))
(Slist <- lapply(seq(nrow(S)), function(i) xpndMat(S[i,])))
t(sapply(Slist,vechMat))