Compute Z^T Z without forming Z explicitly.

Compute Z^T Z without forming Z explicitly.

Usage

gram_ZZ(Zop, block_size = 128L)

Arguments

Zop

Operator as returned by `make_Zop_from_Ks` or similar.

block_size

Number of identity columns processed per batch.

Value

Symmetric dense matrix of size r x r.

Examples

# \donttest{
library(Matrix)
K1 <- Matrix(rnorm(20), 10, 2)
K2 <- Matrix(rnorm(20), 10, 2)
Zop <- make_Zop_from_Ks(list(K1, K2))
G <- gram_ZZ(Zop)
# }