From f63edc4f6f92b3fc7d8323241568754ef7c2f041 Mon Sep 17 00:00:00 2001
From: mashimo <mashimo9000@yahoo.de>
Date: Sun, 26 Apr 2015 15:01:53 +0200
Subject: [PATCH] finished assignment

---
 cachematrix.R | 82 ++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 75 insertions(+), 7 deletions(-)

diff --git a/cachematrix.R b/cachematrix.R
index a50be65aa44..8109e4a2921 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,15 +1,83 @@
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
+## This function creates and stores a special "matrix" object that can cache its inverse.
+## the object is a list of four functions
 
 makeCacheMatrix <- function(x = matrix()) {
-
+    # store the value of the matrix
+  m <- NULL
+  set <- function(y) {
+    x <<- y
+    m <<- NULL
+  }
+  
+    # retrieve the value of the matrix
+  get <- function() x
+  
+    # store the value of the mean
+  setInverse <- function(inverse) m <<- inverse
+  
+    # retrieve the value of the mean
+  getInverse <- function() m
+  
+    # create and store the object: a list containing the 4 functions defined above
+  list(set = set, get = get,
+       setInverse = setInverse,
+       getInverse = getInverse)
+  
 }
 
 
-## Write a short comment describing this function
+## This function computes the inverse of a "matrix" 
+## If the inverse has already been calculated (and the matrix has not changed), then the cachesolve retrieves the inverse from the cache.
+## Return a matrix that is the inverse of 'x'
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+    # first check to see if the inverse matrix has already been calculated and is cached
+  inv <- x$getInverse()
+  print(inv)
+  if(!is.null(inv)) {
+    message("Found in cache.")
+    return(inv)   # retrieve and return immediately
+  } else
+  {
+      # not yet cached: calculate the inverse of the input matrix 
+    message("Not found in cache. Calculating it")
+    data <- x$get()
+    inv <- solve(data)
+    # and set the value of the inverse matrix in the cache via the setInverse function.
+    x$setInverse(inv)
+    # return the calculated inverse matrix
+    return(inv)
+  }
+}
+
+## =========================================================================================
+## This function is used only to test that the above code is working as supposed
+##
+## Test basic caching
+##
+
+unitTestCacheMatrix  <- function() {
+  print("Start ... test matrix is: ")
+  testMatrix <- matrix(c(1, 2, 3, 4), nrow=2, ncol=2)
+  print(testMatrix)
+  
+    # Testing set() and get(): create the special matrix object with caching functions
+  matrixCached <- makeCacheMatrix(testMatrix)
+  print("Get. This is what has been cached: ")
+  print (matrixCached$get())
+  
+    # Test cacheSolve(); now invert the test matrix
+  inverseMatrix <- cacheSolve(matrixCached)
+  print("The matrix inversed is: ")
+  print (inverseMatrix)
+  print("multiplying the test matrix with its inverse should return the identity matrix: ")
+  print(testMatrix %*% inverseMatrix)
+  
+    # Test caching mechanism. Now calculating again. It should found it in the cache
+  print("Now calculating again. It should found it in the cache")
+  againMatrix <- cacheSolve(matrixCached)
+  
+  if (!identical(inverseMatrix, againMatrix))
+    message("Cached version does not match solved version")
 }
+