Matrix Diagonals

Description

Extract or replace the diagonal of a matrix, or construct a diagonal matrix.

Usage

diag(x, nrow, ncol)
diag(x) <- value

Value

If x is a matrix then diag(x) returns the diagonal of x. The resulting vector will have names if the matrix x has matching column and row names.

If x is a vector (or a 1-d array) then diag(x) returns a diagonal matrix whose diagonal is x. If x is an integer then diag(x) returns an identity matrix of order x. The dimension of the returned matrix can be specified by nrow and ncol (the default is square).

The assignment form sets the diagonal of the matrix x to the given value(s).

See Also

matrix.

Examples

dim(diag(3))
diag(10,3,4) # guess what?
all(diag(1:3) == {m <- matrix(0,3,3); diag(m) <- 1:3; m})

diag(var(M <- cbind(X=1:5, Y=rnorm(5))))#-> vector with names "X" and "Y"
rownames(M) <- c(colnames(M),rep("",3));
M; diag(M) #  named as well