cachematrix.R

## The function, makeCacheMatrix creates a special "matrix" => 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 of the matrix
## 4) get the value of the inverse of the matrix

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


## This function calculates the inverse of the special "matrix" created with the above function. 
## However, it first checks to see if the inverse has already been calculated. 
## If so, it gets the inverse from the cache and skips the computation. 
## Otherwise, it calculates the inverse of the data and sets the value of the inverse in the cache via the setinv function.
## This function assumes that the input matrix is invertible.

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