my w3 programming assignment

Author: WilsonTW

cachematrix.R

@@ -1,15 +1,35 @@
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
+## 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(inverse) inv <<- inverse
+    getinverse <- function() inv
+    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. 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'
+    ## Return a matrix that is the inverse of 'x'
+    inv <- x$getinverse()
+    if (!is.null(inv)) {
+        message("getting cached data")
+        return(inv)
+    }
+    mat <- x$get()
+    inv <- solve(mat, ...)
+    x$setinverse(inv)
+    inv
 }