My solution for the Programming Assignment 2

cachematrix.R

@@ -1,15 +1,47 @@
-## Put comments here that give an overall description of what your
-## functions do
+## R Programming - Week 3 - Programming Assignment 2
+##
+## This code file contains 2 functions, makeCacheMatrix and cacheSolve,
+## which are meant to be used the following way :
+##
+## 1. create a matrix object, for example : x <- matrix(rnorm(100, 1), 10, 10)
+## 2. list <- makeCacheMatrix(x)
+## 3. cacheSolve(list)
 
-## Write a short comment describing this function
+## The makeCacheMatrix function creates & returns a special list containing 4 functions
+##
+## 1. set : sets the content of the matrix which we'll calculate the inverse of
+## 2. get : gets the content of the matrix
+## 3. setInv : sets the cached value of the matrix inverse
+## 4. getInv : gets the cached value of the matrix inverse
 
 makeCacheMatrix <- function(x = matrix()) {
-
+        i <- NULL    # inverse variable
+        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 cacheSolve function computes and returns a matrix that is the inverse of 'x'
+## but only if the inverse has not already been calculated (i.e. i = NULL)
+## or if the matrix has changed since the last inverse computation (which sets i as NULL)
+## otherwise the function retrieves the cached inverse value using the get function
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+        i <- x$getInv()
+        if(!is.null(i)) { # this tests if the inverse i has already been computed and if matrix has changed
+                message("Cached data available and the matrix has not changed. Getting cached inverse.")
+                return(i)
+        }
+        else message("No cached data available or the matrix has changed. Calculating the inverse and caching it.")
+        data <- x$get()
+        i <- solve(data, ...)
+        x$setInv(i)
+        i
 }