| symm.prod {fastmatrix} | R Documentation |
Given the order of a symmetrizer and matrix x, performs one of the matrix-matrix
operations:
\bold{Y} = \bold{NX}, if side = "left", or
\bold{Y} = \bold{XN}, if side = "right",
where \bold{N} is the symmetrizer matrix of order n. The main aim of
symm.prod is to do this matrix multiplication without forming the
symmetrizer matrix.
symm.prod(n = 1, x = NULL, side = "left")
n |
order of the symmetrizer matrix. |
x |
numeric matrix (or vector). |
side |
a string selecting if symmetrizer matrix is pre-multiplying |
Underlying C code only uses information provided by symm.info to
performs the matrix multiplication. The symmetrizer matrix is never created.
N4 <- symmetrizer(n = 4, matrix = TRUE) x <- matrix(1:32, ncol = 2) y <- N4 %*% x z <- symm.prod(n = 4, x) # N4 is not stored all(z == y) # matrices y and z are equal!