R: isTriangular() and isDiagonal() Methods

isTriangular {Matrix}

R Documentation

isTriangular() and isDiagonal() Methods

Description

isTriangular(M) returns a logical indicating if M is a triangular matrix. Analogously, isDiagonal(M) is true iff M is a diagonal matrix.

Contrary to isSymmetric(), these two functions are generically from package Matrix, and hence also define methods for traditional (class "matrix") matrices.

Usage

isDiagonal(object)

isTriangular(object, upper = NA, ...)

Arguments

`object`	any R object, typically a matrix (traditional or Matrix package).
`upper`	logical, one of `NA` (default), `FALSE`, or `TRUE` where the last two cases require a lower or upper triangular `object` to result in `TRUE`.
`...`	potentially further arguments for other methods.

Value

a (“scalar”) logical, TRUE or FALSE, never NA. For isTriangular(), if the result is TRUE, it may contain an attribute (see attributes "kind", either "L" or "U" indicating if it is a lower or upper triangular matrix.

Examples

isTriangular(Diagonal(4))
## is TRUE: a diagonal matrix is also (both upper and lower) triangular
(M <- Matrix(c(1,2,0,1), 2,2))
isTriangular(M) # TRUE (*and* of formal class "dtrMatrix")
isTriangular(as(M, "dgeMatrix")) # still triangular, even if not "formally"
isTriangular(crossprod(M)) # FALSE

isDiagonal(matrix(c(2,0,0,1), 2,2)) # TRUE