cachematrix.R

## write a pair of functions that cache the inverse of a matrix

## makeCacheMatrix: This function creates a special "matrix" object 
## that can cache its inverse.
makeCacheMatrix <- function(x = matrix()) {
  inv_x <- NULL
  set <- function(y) {
    x <<- y
    inv_x <<- NULL
  }
  get <- function() x
  setinverse <- function(inverse) inv_x <<-inverse
  getinverse <- function() inv_x
  list(set = set, get = get,
       setinverse = setinverse,
       getinverse = getinverse)
}

## cacheSolve: This function computes the inverse of the special 
## "matrix" returned by makeCacheMatrix above. 
## If the inverse has already been calculated, 
## then the cachesolve should retrieve the inverse from the cache.
cacheSolve <- function(x, ...) {
        ## Return a matrix that is the inverse of 'x'
  inv_x <- x$getinverse()
  if (!is.null(inv_x)) {
    message("getting cached inverse matrix")
    return(inv_x)
  } else {
    inv_x <- solve(x$get())
    x$setinverse(inv_x)
    return(inv_x)
  }
}

# test
# m <- makeCacheMatrix(matrix(1:4, 2, 2))
# m$get()
# m$$getInverse()
# cacheSolve(m)
# cacheSolve(m)