Cross-product between a Filebacked Big Matrix and a matrix.

big_cprodMat(
X,
A.row,
ind.row = rows_along(X),
ind.col = cols_along(X),
ncores = 1,
block.size = block_size(nrow(X)),
center = NULL,
scale = NULL
)

# S4 method for FBM,matrix
crossprod(x, y)

# S4 method for FBM,matrix
tcrossprod(x, y)

# S4 method for matrix,FBM
crossprod(x, y)

# S4 method for matrix,FBM
tcrossprod(x, y)

## Arguments

X An object of class FBM. A matrix with length(ind.row) rows. An optional vector of the row indices that are used. If not specified, all rows are used. Don't use negative indices. An optional vector of the column indices that are used. If not specified, all columns are used. Don't use negative indices. Number of cores used. Default doesn't use parallelism. You may use nb_cores. Maximum number of columns read at once. Default uses block_size. Vector of same length of ind.col to subtract from columns of X. Vector of same length of ind.col to divide from columns of X. A 'double' FBM or a matrix. A 'double' FBM or a matrix.

## Value

$$X^T \cdot A$$.

## Matrix parallelization

Large matrix computations are made block-wise and won't be parallelized in order to not have to reduce the size of these blocks. Instead, you may use Microsoft R Open or OpenBLAS in order to accelerate these block matrix computations. You can also control the number of cores used with bigparallelr::set_blas_ncores().

## Examples

X <- big_attachExtdata()
n <- nrow(X)
m <- ncol(X)
A <- matrix(0, n, 10); A[] <- rnorm(length(A))

test <- big_cprodMat(X, A)
true <- crossprod(X[], A)
all.equal(test, true)#>  TRUE
X2 <- big_copy(X, type = "double")
all.equal(crossprod(X2, A), true)#>  TRUE
# subsetting
ind.row <- sample(n, n/2)
ind.col <- sample(m, m/2)

tryCatch(test2 <- big_cprodMat(X, A, ind.row, ind.col),
error = function(e) print(e))#> <simpleError: Incompatibility between dimensions.># returns an error. You need to use the subset of A:
test2 <- big_cprodMat(X, A[ind.row, ], ind.row, ind.col)
true2 <- crossprod(X[ind.row, ind.col], A[ind.row, ])
all.equal(test2, true2)#>  TRUE