R: Force a Matrix to 'symmetricMatrix' Without Symmetry Checks

forceSymmetric {Matrix}

R Documentation

Force a Matrix to 'symmetricMatrix' Without Symmetry Checks

Description

Force a square matrix x to a symmetricMatrix, without a symmetry check as it would be applied for as(x, "symmetricMatrix").

Usage

forceSymmetric(x, uplo)

Arguments

`x`	any square matrix (of numbers), either “"traditional"” (`matrix`) or inheriting from `Matrix`.
`uplo`	optional string, `"U"` or `"L"` indicating which “triangle” half of `x` should determine the result. The default is `"U"` unless `x` already has a `uplo` slot (i.e., when it is `symmetricMatrix`, or `triangularMatrix`), where the default will be `x@uplo`.

Value

a square matrix inheriting from class symmetricMatrix.

Examples

 ## Hilbert matrix
 i <- 1:6
 h6 <- 1/outer(i - 1L, i, "+")
 sd <- sqrt(diag(h6))
 hh <- t(h6/sd)/sd # theoretically symmetric
 isSymmetric(hh, tol=0) # FALSE; hence
 try( as(hh, "symmetricMatrix") ) # fails, but this works fine:
 H6 <- forceSymmetric(hh)

 ## result can be pretty surprising:
 (M <- Matrix(1:36, 6))
 forceSymmetric(M) # symmetric, hence very different in lower triangle
 (tm <- tril(M))
 forceSymmetric(tm)