Implement the cached inverse matrix

Author: yn

cachematrix.R

@@ -1,15 +1,41 @@
-## Put comments here that give an overall description of what your
-## functions do
+## Together, these functions create a special "matrix" object that can cache its inverse.
 
-## Write a short comment describing this function
+## The function makeCacheMatrix implements the storage of special "matrix" object.
+## It returns a list of closures that capture the variables x and i,
+## where x is the matrix being stored, and i is the cached inverse.
+## The four closures returned perform the following operations:
+## 1. set the matrix. This clears the cached inverse
+## 2. get the matrix
+## 3. set the cached inverse
+## 4. get the cached inverse
 
 makeCacheMatrix <- function(x = matrix()) {
-
+  i <- NULL
+  set <- function(y) {
+    x <<- y
+    i <<- NULL
+  }
+  get <- function() x
+  setinv <- function(inv) i <<- inv
+  getinv <- function() i
+  list(set = set, get = get,
+       setinv = setinv,
+       getinv = getinv)
 }
 
-
-## Write a short comment describing this function
+## The function cacheSolve returns the inverse of a matrix.
+## It either returns it from the cache if it's 
+## been called previously, or calculates a new one
+## and caches it.
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+  i <- x$getinv()
+  if(!is.null(i)) {
+    message("getting cached data")
+    return(i)
+  }
+  data <- x$get()
+  i <- solve(data, ...)
+  x$setinv(i)
+  i
 }