submit the exercise function

Author: jjww2015

Diff for: cachematrix.R

@@ -1,15 +1,54 @@
-## Put comments here that give an overall description of what your
-## functions do
+## Matrix inversion is potentially time-consuming, particullarly when repeated 
+## inversion must be performed on the same matrix. This function is to creates 
+## a special "matrix" object that can cache its inverse  If the inverse has 
+## already been calculated (and the matrix has not changed), then this function 
+##retrieve the inverse from the cache without repeating the operation. 
 
-## Write a short comment describing this function
+## This function creates a special "matrix" object that can cache its inverse.
 
 makeCacheMatrix <- function(x = matrix()) {
-
+    # Creates a special "matrix" object that can cache its inverse.
+    #
+    # Args:
+    #   x: One matrix used to initialize the cacheMatrix object.
+    #
+    # Returns:
+    #   An object that can cache the inverse of the input matrix.
+    invx <- NULL
+    set <- function(y) {
+        x <<- y
+        invx <<- NULL
+    }
+    get <- function() x
+    setMatrixInverse <- function(invMatrix) invx <<- invMatrix
+    getMatrixInverse <- function() invx
+    list(set = set, get = get,
+         setMatrixInverse = setMatrixInverse,
+         getMatrixInverse = getMatrixInverse)
 }
 
-
-## 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'
+    # Creates a special "matrix" object that can cache its inverse.
+    #
+    # Args:
+    #   x: matrix object that can cache its inverse. 
+    #
+    # Returns:
+    #   the inverse of the matrix.
+    
+    ## Return a matrix that is the inverse of 'x'
+    invx <- x$getMatrixInverse()
+    if(!is.null(invx)) {
+        message("getting cached inversed matrix")
+        return(invx)
+    }
+    data <- x$get()
+    invx <- solve(data, ...)
+    x$setMatrixInverse(invx)
+    invx
 }