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

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