From 3b0447e9f849cc6c9c6b6df78388104b2635de95 Mon Sep 17 00:00:00 2001
From: h-s <hsuwanda@googlemail.com>
Date: Mon, 21 Apr 2014 17:52:18 -0400
Subject: [PATCH 1/2] Initial commit for Assignment 2

---
 cachematrix.R | 55 ++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 48 insertions(+), 7 deletions(-)

diff --git a/cachematrix.R b/cachematrix.R
index a50be65aa44..73c456159a2 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,15 +1,56 @@
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
+## This function is the constructor for a "special" matrix that is able
+## to save its inverse in the cache to avoid repeated calculations.
+## It provides four methods for getting and setting the matrix and its inverse.
+##
+## The get() method will return the matrix to be inverted.
+## The set(x) method will set a new matrix to be inverted and clear the cache.
+## The getinv() method will return the inverse matrix from the cache
+## The setinv(inv) method will save the inverse matrix in the cache
 
 makeCacheMatrix <- function(x = matrix()) {
-
+    xinv <- NULL
+    
+    get <- function() {
+        x
+    }
+    
+    set <- function(y) {
+        x <<- y
+        xinv <<- NULL
+    }
+    
+    getinv <- function() {
+        xinv
+    }
+    
+    setinv <- function(inv) {
+        xinv <<- inv
+    }
+    
+    list(get = get, set = set, getinv = getinv, setinv = setinv)
 }
 
 
-## Write a short comment describing this function
+## This function returns the inverse matrix of the "special" matrix
+## constructed by the above makeCacheMatrix() constructor.
+## The special matrix is passed as the argument x.
+## If the inverse matrix is available in the cache, a message will
+## be printed. 
+## Otherwise the inverse matrix will be computed and saved in the cache.
+## It is assumed that the matrix is always invertible
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+    ## Try to retrieve the inverse from cache 
+    inv <- x$getinv()
+    if (!is.null(inv)) {
+        message("Getting cache data")
+    }
+    else {
+        ## inverse matrix is not available yet
+        ## retrieve matrix, compute its inverse, and save it in cache
+        matrix <- x$get()
+        inv <- solve(matrix)
+        x$setinv(inv)
+    }
+    inv
 }

From f5b62e9a8ebd4b18307e91d9777c3796aab0976b Mon Sep 17 00:00:00 2001
From: h-s <hsuwanda@googlemail.com>
Date: Mon, 21 Apr 2014 18:05:27 -0400
Subject: [PATCH 2/2] Second commit for Assignment 2

---
 cachematrix.R | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/cachematrix.R b/cachematrix.R
index 73c456159a2..038ca36c80d 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,11 +1,15 @@
 ## This function is the constructor for a "special" matrix that is able
-## to save its inverse in the cache to avoid repeated calculations.
+## to save its inverse in the cache to avoid unnecessary recalculations.
 ## It provides four methods for getting and setting the matrix and its inverse.
+## - get() method will return the matrix to be inverted.
+## - set(x) method will set a new matrix to be inverted and clear the cache.
+## - getinv() method will return the inverse matrix from the cache
+## - setinv(inv) method will save the inverse matrix in the cache
 ##
-## The get() method will return the matrix to be inverted.
-## The set(x) method will set a new matrix to be inverted and clear the cache.
-## The getinv() method will return the inverse matrix from the cache
-## The setinv(inv) method will save the inverse matrix in the cache
+## Once an object is created by this constructor, you may change the underlying
+## matrix to be inverted by the set() method. This will clear the cache, 
+## and a new inverse matrix must be computed the next time via cacheSolve().
+
 
 makeCacheMatrix <- function(x = matrix()) {
     xinv <- NULL