rkeops (version 2.2.2)

matmult.default: 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 of the same length, it will return the inner product (as a matrix).

Usage

# S3 method for default
%*%(x, y)

Value

A double or complex matrix product. Use drop to remove dimensions which have only one level.

Arguments

x, y

numeric or complex matrices or vectors.

Author

R core team and contributors

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.

See Also

base::matmult

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