Programming Assignment 2: Lexical Scoping

2014.07.27 rdpeng#1
Committing "Programming Assignment 2: Lexical Scoping" R file into my
git repository

Author: DavoodQorbani

cachematrix.R

@@ -1,15 +1,53 @@
-## Put comments here that give an overall description of what your
-## functions do
+## Below are two functions that are used to create a special object
+## that stores a matrix and cache's its inverse.
+## (We assume that the matrix supplied is always invertible.)
 
-## Write a short comment describing this function
 
-makeCacheMatrix <- function(x = matrix()) {
+## The first function creates a special "matrix" object that can cache its inverse.
+## Example:
+## For the sake of fun, run the following in your R console:
+## > rpeng <- makeCacheMatrix(matrix(1:4, 2, 2))
+## (This is an example. You can change "rpeng" or the content of the square matrix as you wish!)
+## Till now, the inverse has not been calculated. To make sure, you can run the following:
+## > rpeng$getSolve()
+## As you see, you get a matrix with NA values.
 
+makeCacheMatrix <- function(x = matrix()) {
+        s <- matrix(NA, nrow(x), nrow(x))
+        set <- function(y) {
+                x <<- y
+                s <<- matrix(NA, nrow(x), nrow(x))
+        }
+        get <- function() x
+        setSolve <- function(solve) s <<- solve
+        getSolve <- function() s
+        list(set = set, get = get,
+             setSolve = setSolve,
+             getSolve = getSolve)
 }
 
 
-## Write a short comment describing this function
+## The second 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 the cachesolve should retrieve the inverse from the cache
+
+## Example (Continued):
+## Run the following:
+## > cacheSolve(rpeng)
+## You will see the inverse.
+## If you run the above command again (it means that you have not changed the matrix),
+## you will see this message: "getting cached data" and the cached inverse matrix.
 
 cacheSolve <- function(x, ...) {
         ## Return a matrix that is the inverse of 'x'
-}
+        s <- x$getSolve()
+        if(!anyNA(s)) {
+                message("getting cached data")
+                return(s)
+                invisible(x)
+        }
+        data <- x$get()
+        s <- solve(data, ...)
+        x$setSolve(s)
+        s
+}