(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
m <- matrix(1:6, 2,3) ; v <- 1:3; v2 <- 2:1
stopifnot(identical(tcrossprod(v, m), v %*% t(m)),
identical(tcrossprod(v, m), crossprod(v, t(m))),
identical(crossprod(m, v2), t(m) %*% v2))
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