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assessment3.R

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+# See README.md for instructions on running the code and output from it
+# The assignment states that running the code is not part of the grading 
+# but I have the instructions anyway.
+
+# makeCacheMatrix is a function that returns a list of functions
+# Its puspose is to store a martix and a cached value of the inverse of the 
+# matrix. Contains the following functions:
+# * setMatrix      set the value of a matrix
+# * getMatrix      get the value of a matrix
+# * cacheInverse   get the cahced value (inverse of the matrix)
+# * getInverse     get the cahced value (inverse of the matrix)
+#
+# Notes:
+# not sure how the "x = numeric()" part works in the argument list of the 
+# function, but it seems to be creating a variable "x" that is not reachable 
+# from the global environment, but is available in the environment of the 
+# makeCacheMatrix function
+makeCacheMatrix <- function(x = numeric()) {
+
+        # holds the cached value or NULL if nothing is cached
+        # initially nothing is cached so set it to NULL
+        cache <- NULL
+
+        # store a matrix
+        setMatrix <- function(newValue) {
+                x <<- newValue
+                # since the matrix is assigned a new value, flush the cache
+                cache <<- NULL
+        }
+
+        # returns the stored matrix
+        getMatrix <- function() {
+                x
+        }
+
+        # cache the given argument 
+        cacheInverse <- function(solve) {
+                cache <<- solve
+        }
+
+        # get the cached value
+        getInverse <- function() {
+                cache
+        }
+
+        # return a list. Each named element of the list is a function
+        list(setMatrix = setMatrix, getMatrix = getMatrix, cacheInverse = cacheInverse, getInverse = getInverse)
+}
+
+
+# The following function calculates the inverse of a "special" matrix created with 
+# makeCacheMatrix
+cacheSolve <- function(y, ...) {
+        # get the cached value
+        inverse <- y$getInverse()
+        # if a cached value exists return it
+        if(!is.null(inverse)) {
+                message("getting cached data")
+                return(inverse)
+        }
+        # otherwise get the matrix, caclulate the inverse and store it in
+        # the cache
+        data <- y$getMatrix()
+        inverse <- solve(data)
+        y$cacheInverse(inverse)
+
+        # return the inverse
+        inverse
+}