facmul {Matrix} R Documentation

## Multiplication by Decomposition Factors

### Description

Performs multiplication by factors for certain decompositions (and allows explicit formation of those factors).

### Usage

facmul(x, factor, y, transpose, left, ...)


### Arguments

 x a matrix decomposition. No missing values or IEEE special values are allowed. factor an indicator for selecting a particular factor for multiplication. y a matrix or vector to be multiplied by the factor or its transpose. No missing values or IEEE special values are allowed. transpose a logical value. When FALSE (the default) the factor is applied. When TRUE the transpose of the factor is applied. left a logical value. When TRUE (the default) the factor is applied from the left. When FALSE the factor is applied from the right. ... the method for "qr.Matrix" has additional arguments.

### Value

the product of the selected factor (or its transpose) and y

### NOTE

Factors for decompositions such as lu and qr can be stored in a compact form. The function facmul allows multiplication without explicit formation of the factors, saving both storage and operations.

### References

Golub, G., and Van Loan, C. F. (1989). Matrix Computations, 2nd edition, Johns Hopkins, Baltimore.

### Examples

library(Matrix)
x <- Matrix(rnorm(9), 3, 3)
## Not run:
qrx <- qr(x)                      # QR factorization of x
y <- rnorm(3)
facmul( qr(x), factor = "Q", y)   # form Q y

## End(Not run)


[Package Matrix version 1.4-1 Index]