[R] triangular matrices input/output

[Rui Barradas]

Hello,

I needed this once.

upper.diag <- function(x, byrow=FALSE){
	m <- sqrt(1 + 8*length(x))
	if(abs(m - floor(m)) <  .Machine$double.eps^0.5)
		m <- (m - 1)/2
	else{
		warning("length of 'x' is not a triangular number.")
		m <- floor((m - 1)/2)
	}
	y <- matrix(0, nrow=m, ncol=m)
	if(byrow){
		y[lower.tri(y, TRUE)] <- x
		y <- t(y)
	}else
		y[upper.tri(y, TRUE)] <- x
	y
}

lower.diag <- function(x, byrow=FALSE){
	m <- sqrt(1 + 8*length(x))
	if(abs(m - floor(m)) <  .Machine$double.eps^0.5)
		m <- (m - 1)/2
	else{
		warning("length of 'x' is not a triangular number.")
		m <- floor((m - 1)/2)
	}
	y <- matrix(0, nrow=m, ncol=m)
	if(byrow){
		y[upper.tri(y, TRUE)] <- x
		y <- t(y)
	}else
		y[lower.tri(y, TRUE)] <- x
	y
}

lower.diag(1:6)
lower.diag(1:10, TRUE)
lower.diag(1:8)

upper.diag(1:6)
upper.diag(1:10, TRUE)
upper.diag(1:12)

Hope this helps,

Rui Barradas

casperyc wrote
> 
> Hi,
> 
> Is there any package that deals with triangular matrices?
> 
> Say ways of inputting an upper (lower) triangular matrix?
> 
> Or convert a vector of length 6 to an upper (lower) triangular matrix (by
> row/column)?
> 
> Thanks!
> 
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