cachematrix.R

## A pairs of function to chache matrix's inverse, 
## if inverse has already been calculated,
## then the inverse should be retrieve from cache

## This function creates a special "matrix" object
## that can cache its inverse.

makeCacheMatrix <- function(x = matrix()) {
  inv <- NULL
  set <- function(y) {
    x <<- y
    inv <<- NULL
  }
  get <- function() x
  setinverse <- function(solve) inv <-- solve
  getinverse <- function() inv
  list(set = set, get = get,
       setinverse = setinverse,
       getinverse = getinverse)

}


## 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 cacheSolve should retrieve the inverse from the cache.

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