diff --git a/cachematrix.R b/cachematrix.R
index a50be65aa44..3357a1c9e60 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,15 +1,41 @@
-## Put comments here that give an overall description of what your
-## functions do
+## Caching the Inverse of a Matrix.
 
-## Write a short comment describing this function
+## This function creates a special "matrix" object that can cache 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)
 }
 
 
-## Write a short comment describing this function
+## This function computes the inverse of the special "matrix" returned by makeCacheMatrix above.
 
 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
 }
+
+
+## usage:
+## x <- matrix(rnorm(10000), c(100, 100))
+## xx <- makeCacheMatrix(x)
+## cacheSolve(xx)
+## # two times
+## cacheSolve(xx)