| matmult {base} | R Documentation |
Matrix Multiplication
Description
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 it will return the inner product.
Usage
a %*% b
Arguments
a, b |
numeric or complex matrices or vectors. |
Details
When a vector is promoted to a matrix, its names are not
promoted to row or column names, unlike as.matrix.
Value
The matrix product. Use drop to get rid of dimensions
which have only one level.
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth \& Brooks/Cole.
See Also
matrix,
Arithmetic,
diag.
Examples
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