| crossprod {base} | R Documentation |
Given matrices x and y as arguments, return a matrix
cross-product. This is formally equivalent to (but usually slightly
faster than) the call t(x) %*% y (crossprod) or
x %*% t(y) (tcrossprod).
crossprod(x, y = NULL) tcrossprod(x, y = NULL)
x, y |
numeric or complex matrices: y = NULL is taken to
be the same matrix as x. Vectors are promoted to
single-column matrices. |
A double or complex matrix, with appropriate dimnames taken
from x and y.
When x or y are not matrices, they are treated as column or
row matrices, but their names are usually not
promoted to dimnames. Hence, currently, the last
example has empty dimnames.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
(z <- crossprod(1:4)) # = sum(1 + 2^2 + 3^2 + 4^2)
drop(z) # scalar
x <- 1:4; names(x) <- letters[1:4]; x
tcrossprod(as.matrix(x)) # is
identical(tcrossprod(as.matrix(x)),
crossprod(t(x)))
tcrossprod(x) # no dimnames