klin.preparels: Prepares matrices for the least squares solver
In klin: Linear equations with Kronecker structure

Description Usage Arguments Details Value Author(s) See Also Examples

You should use this function whenever you are calling klin.ls repeatedly with the same matrices.

1	klin.preparels(A)

`A`	A list that contains the matrices, preferably of class `Matrix`.

To compute the least squares estimate, we are solving

(A_1 \times A_2 … \times A_K)^T (A_1 \times A_2 \times … \times A_K) = (A_1 \times A_2 \times … \times A_K)^T b

However, for square A_i matrices, one can premultiply both sides by the Kronecker product of the inverse of $A_i^T$ (in the corresponding place) and identity matrices, making the problem simpler.

klin.prepls calculates the matrices needed on both sides, but does not evaluate the Kronecker product.

A list of class klin.prepls, contains matrices for the left and right hand side.

Tamas K Papp <tpapp@princeton.edu>

klin.eval, klin.solve, klin.ls, klin.klist.

## dimensions
n <- c(2,4,3)
m <- n+c(1,0,2)			# we need m >= n
## make random matrices
A <- lapply(seq_along(n),
            function(i) Matrix(rnorm(m[i]*n[i]),m[i],n[i]))
b <- rnorm(prod(m))		# make random b
prepA <- klin.preparels(A)
x <- klin.ls(prepA,b)