# daxpy: BLAS daxpy functionality In bigalgebra: BLAS routines for native R matrices and big.matrix objects.

## Description

This function implements the function Y := A * X + Y where X and Y may be either native double-precision valued R matrices or numeric vectors, or double-precision valued `big.matrix` objects, and A is a scalar.

## Usage

 `1` ```daxpy(A=1, X, Y) ```

## Arguments

 `A` Optional numeric scalar value to scale the matrix `X` by, with a default value of 1. `X` Requried to be either a native R `matrix` or numeric vector, or a `big.matrix` object `Y` Optional native R `matrix` or numeric vector, or a `big.matrix` object

## Details

At least one of either `X` or `Y` must be a `big.matrix`. All values must be of type `double` (the only type presently supported by the bigalgebra package).

This function is rarely necessary to use directly since the bigalgebra package defines standard arithmetic operations and scalar multiplication. It is more efficient to use `daxpy` directly when both scaling and matrix addition are required, in which case both operations are performed in one step.

## Value

The output value depends on the classes of input values `X` and `Y` and on the value of the global option `bigalgebra.mixed_arithmetic_returns_R_matrix`.

If `X` and `Y` are both big matrices, or `Y` is missing, `options("bigalgebra.mixed_arithmetic_returns_R_matrix")` is `FALSE`, then a `big.matrix` is returned. The returned `big.matrix` is backed by a temporary file mapping that will be deleted when the returned result is garbage collected by R (see the examples).

Otherwise, a standard R matrix is returned. The dimensional shape of the output is taken from `X`. If input `X` is dimensionless (that is, lacks a dimension attribute), then the output is a column vector.

Michael J. Kane

## References

`bigmemory`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16``` ```require(bigmemory) A = matrix(1, nrow=3, ncol=2) B = big.matrix(nrow=3, ncol=2, type='double', init=1) C = B + B # C is a new big matrix D = A + B # D defaults to a regular R matrix, to change this, set the option: # optons(bigalgebra.mixed_arithmetic_returns_R_matrix=FALSE) E = daxpy(A=1.0, X=B, Y=B) # Same kind of result as C print(C[]) print(D) print(E[]) # The C and E big.matrix file backings will be deleted when garbage collected: # (We enable debugging to see this explicitly) options(bigalgebra.DEBUG=TRUE) rm(C,E) gc() ```