Matrix and invertible function

Author: MichaelNowell

cachematrix.R

@@ -1,16 +1,63 @@
-##Second GIT Project
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
-
 makeCacheMatrix <- function(x = matrix()) {
-
+  ## @x: a square invertible matrix
+  ## return: a list containing functions to
+  ##              1. set the matrix
+  ##              2. get the matrix
+  ##              3. set the inverse
+  ##              4. get the inverse
+  ##         this list is used as the input to cacheSolve()
+  
+  inv = NULL
+  set = function(y) {
+    # use `<<-` to assign a value to an object in an environment 
+    # different from the current environment. 
+    x <<- y
+    inv <<- NULL
+  }
+  get = function() x
+  setinv = function(inverse) inv <<- inverse 
+  getinv = function() inv
+  list(set=set, get=get, setinv=setinv, getinv=getinv)
 }
 
+cacheSolve <- function(x, ...) {
+  ## @x: output of makeCacheMatrix()
+  ## return: inverse of the original matrix input to makeCacheMatrix()
+  
+  inv = x$getinv()
+  
+  # if the inverse has already been calculated
+  if (!is.null(inv)){
+    # get it from the cache and skips the computation. 
+    message("getting cached data")
+    return(inv)
+  }
+  
+  # otherwise, calculates the inverse 
+  mat.data = x$get()
+  inv = solve(mat.data, ...)
+  
+  # sets the value of the inverse in the cache via the setinv function.
+  x$setinv(inv)
+  
+  return(inv)
+}
 
-## Write a short comment describing this function
+##Test function
 
-cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+test = function(mat){
+  ## @mat: an invertible matrix
+  
+  temp = makeCacheMatrix(mat)
+  
+  start.time = Sys.time()
+  cacheSolve(temp)
+  dur = Sys.time() - start.time
+  print(dur)
+  
+  start.time = Sys.time()
+  cacheSolve(temp)
+  dur = Sys.time() - start.time
+  print(dur)
 }
+