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).
Value
A double or complex matrix product. Use drop to remove
dimensions which have only one level.
Details
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 a generic function: methods can be written for it
individually or via the matOps group
generic function; it dispatches to S3 and S4 methods. Methods need to be
written for a function that takes two arguments named x and y.
Examples
x <- 1:4
(z <- x %*% x) # scalar ("inner") product (1 x 1 matrix)
#> [,1]
#> [1,] 30
drop(z) # as scalar
#> [1] 30
y <- diag(x)
z <- matrix(1:12, ncol = 3, nrow = 4)
y %*% z
#> [,1] [,2] [,3]
#> [1,] 1 5 9
#> [2,] 4 12 20
#> [3,] 9 21 33
#> [4,] 16 32 48
y %*% x
#> [,1]
#> [1,] 1
#> [2,] 4
#> [3,] 9
#> [4,] 16
x %*% z
#> [,1] [,2] [,3]
#> [1,] 30 70 110