Implement makeCacheMatrix and cacheSolve

Author: hwartig

cachematrix.R

@@ -1,15 +1,37 @@
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
-
+# makeCacheMatrix creates a special 'matrix' object which can cache its inverse.
 makeCacheMatrix <- function(x = matrix()) {
-
+  m <- NULL
+  set <- function(y) {
+    x <<- y
+    m <<- NULL
+  }
+  get <- function() x
+  setinverse <- function(inverse) m <<- inverse
+  getinverse <- function() m
+  list(
+    set = set,
+    get = get,
+    setinverse = setinverse,
+    getinverse = getinverse
+  )
 }
 
-
-## Write a short comment describing this function
-
-cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+# cacheSolve computes the inverse of the special 'matrix' returned by
+# makeCacheMatrix. If the inverse has already been calculated (and the matrix
+# has not changed), then the cachesolve will retrieve the inverse from the cache.
+#
+# params
+#   x: a cache matrix created with makeCacheMatrix
+cacheSolve <- function(x) {
+  # see https://class.coursera.org/rprog-004/forum/thread?thread_id=993 for an
+  # explanation why I don't allow additional parameters `...`.
+  m <- x$getinverse()
+  if(!is.null(m)) {
+    message("getting cached data")
+    return(m)
+  }
+  data <- x$get()
+  m <- solve(data)
+  x$setinverse(m)
+  m
 }