matmult {base} | R Documentation |
Multiplies two matrices, if they are conformable. If one argument is a vector, it will be promoted to either a row or column matrix to make the two arguments conformable. If both are vectors of the same length, it will return the inner product (as a matrix).
x %*% y
x, y |
numeric or complex matrices or vectors. |
When a vector is promoted to a matrix, its names are not
promoted to row or column names, unlike as.matrix
.
Promotion of a vector to a 1-row or 1-column matrix happens when one
of the two choices allows x
and y
to get conformable
dimensions.
This operator is S4 generic but not S3 generic. S4 methods need to be
written for a function of two arguments named x
and y
.
A double or complex matrix product. Use drop
to remove
dimensions which have only one level.
The propagation of NaN/Inf values, precision, and performance of matrix
products can be controlled by options("matprod")
.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
For matrix crossproducts, crossprod()
and
tcrossprod()
are typically preferable.
matrix
, Arithmetic
, diag
.
x <- 1:4
(z <- x %*% x) # scalar ("inner") product (1 x 1 matrix)
drop(z) # as scalar
y <- diag(x)
z <- matrix(1:12, ncol = 3, nrow = 4)
y %*% z
y %*% x
x %*% z