Add existing file

Author: nickramskill

cachematrix.R

@@ -1,15 +1,61 @@
-## Put comments here that give an overall description of what your
-## functions do
+# R Programming Week 2 Assignment: Lexical Scoping
 
-## Write a short comment describing this function
+# Validation: 
+# m <- matrix(rnorm(4),nrow=2,ncol=2)
+# x <- makeCacheMatrix(m)
+# cacheSolve(x)
+# cacheSolve(x)
 
-makeCacheMatrix <- function(x = matrix()) {
+# Overall these functions create matrices and subsequently move the created matrix to and from 
+# the cache memory and perform operations on the data
 
-}
+m <- matrix(rnorm(4),nrow=2,ncol=2) # creates the 2D square matrix to be inverted in this test
+print(m) # prints the created 2D square matrix to the console
+
+# In principle, makeCacheMatrix creates the list of functions that move the data matrix and the 
+# inverted data matrix to and from the cache memory
 
+makeCacheMatrix <- function(x = numeric()) {
+        invm <- NULL                                   ## initialises a NULL variable for the inverted matrix "invm" in the local memory
+        set <- function(y) {                           ## creates the set function to set the data matrix and invm to the cache memory
+                x <<- y                                ## sets the passed data matrix to cache memory
+                invm <<- NULL                          ## initialises NULL in cache memory
+        }
+        get <- function() x                            ## function to get variable x from cache memory 
+        setinv <- function(solve) invm <<- solve       ## function to set the value of invm in cache memory
+        getinv <- function() invm                      ## get the value of invm from cache memory
+        list(set = set, get = get,                     ## returns list of functions
+             setinv = setinv,
+             getinv = getinv)
+}
 
-## Write a short comment describing this function
+# In pricniple, cacheSolve receives the data matrix (created above in x <- makeCacheMatrix(m)) and checks the cache to see if the 
+# inverse of the matrix (invm) has already been calculated. If so, the value of invm stored in cache is displayed in the console. 
+# If a NULL value is stored in the cache, the data matrix x (stored in cache) will be retrieved and the inverse matrix is calculated.
+# This will then be stored in cache memory and finally be displayed in the console. 
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+        invm <- x$getinv()                            ## retrives the value of invm into local memory from cache memory
+        if(!is.null(invm)) {                          ## NOT logical operator to determine whether inverse has already been calculated
+                message("getting cached data")        ## if NOT null, will display the message "getting cached data" ...
+                return(invm)                          ## ... and print to console
+        }
+        data <- x$get()                               ## if a NULL value of invm is obtained, the data matrix is loaded to local memory
+        invm <- solve(data, ...)                      ## and the inverse calculated using the solve() function
+        x$setinv(invm)                                ## setinv saves the invm to cache memory
+        invm                                          ## ... and print to console
 }
+
+# Example:
+
+# m <- matrix(rnorm(4),nrow=2,ncol=2)
+# > x <- makeCacheMatrix(m)
+# > cacheSolve(x)
+# [,1]      [,2]
+# [1,]  1.0593015 1.6706482
+# [2,] -0.1026943 0.9169256
+# > cacheSolve(x)
+# getting cached data
+# [,1]      [,2]
+# [1,]  1.0593015 1.6706482
+# [2,] -0.1026943 0.9169256