cachematrix.R

## These two functions cache the inverse of a matrix. 
## REQ: the matrix supplied is always invertible.

## This function returns a list of four functions setting/getting the value of a matrix
## and setting/getting the value of its inverse.

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


## This function returns the inverse of a matrix from the above function if it
## has been calculated, calculates and returns the inverse itself otherwise.

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