title	cachematrix
author	Jose Carlos Arriola
date	14 February 2016
output	html_document

Lexical Scoping - My Solution

Matrix inversion is usually a costly computation and there may be some benefit to caching the inverse of a matrix rather than compute it repeatedly (there are also alternatives to matrix inversion that we will not discuss here). In this assignment a pair of functions are implemented that cache the inverse of a matrix: makeCacheMatrix and cacheSolve.

makeCacheMatrix

Creates a special "matrix", which is really a list containing a function to

1. set the value of the matrix
2. get the value of the matrix
3. set the value of the inverse matrix
4. get the value of the inverse matrix

makeCacheMatrix <- function(x = matrix()) {
  inv <- NULL
  set <- function(y) {
    x <<- y
    inv <<- NULL
  }
  get <- function() x
  setinv <- function(i) inv <<- i
  getinv <- function() inv
  list(set = set, get = get,
       setinv = setinv,
       getinv = getinv)
}

cacheSolve

Computes the inverse of the special "matrix" returned by makeCacheMatrix above. If the inverse has already been calculated (and the matrix has not changed), then the cachesolve should retrieve the inverse from the cache.

cacheSolve <- function(x, ...) {
  ## Return a matrix that is the inverse of 'x'
  i <- x$getinv()
  if(!is.null(i)) {
    message("Getting cached data ...")
    return(i)
  }
  data <- x$get()
  i <- solve(data, ...)
  x$setinv(i)
  i
}

Testing

my_matrix <- makeCacheMatrix(matrix(1:4, 2, 2))
my_matrix$get()

>    [,1] [,2]
[1,]    1    3
[2,]    2    4

my_matrix$getinv()

> NULL

cacheSolve(my_matrix)

>     [,1] [,2]
[1,]   -2  1.5
[2,]    1 -0.5

cacheSolve(my_matrix)

> Getting cached data ...
     [,1] [,2]
[1,]   -2  1.5
[2,]    1 -0.5

my_matrix$getinv()

>     [,1] [,2]
[1,]   -2  1.5
[2,]    1 -0.5