Implement caching matrix inverse for assignment

Author: kay-johansen

cachematrix.R

@@ -1,15 +1,46 @@
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
-
-makeCacheMatrix <- function(x = matrix()) {
-
-}
-
-
-## Write a short comment describing this function
-
-cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
-}
+## Class and companion function to store a matrix 
+##   together with its cached inverse
+## Kay Johansen 
+
+## Create an object that contains a matrix
+##   and a place to cache its inverse
+## This object does not calculate the inverse itself;
+##   use the companion function cacheSolve() to do that
+makeCacheMatrix <- function(theMatrix = matrix()) {
+  theInverse <- NULL
+  
+  set <- function(m) {
+    theMatrix <<- m
+    theInverse <<- NULL
+  }
+  
+  get <- function() 
+    theMatrix
+  
+  setInverse <- function(inv) 
+    theInverse <<- inv
+  
+  getInverse <- function(inv)
+    theInverse
+  
+  list(set = set, get = get, setInverse = setInverse, getInverse = getInverse)
+}
+
+
+## Returns the inverse of the matrix contained in the 
+##   cacheMatrix object
+## Uses the cached inverse if it's already cached,
+##   otherwise, calls solve to calculate the inverse
+##   and sets the cached value
+cacheSolve <- function(cacheMatrix, ...) {
+  inv <- cacheMatrix$getInverse()
+  if (!is.null(inv)) {
+    message("cache hit")
+    return(inv)
+  }
+  message("cache miss")
+  m <- cacheMatrix$get()
+  inv <- solve(m)
+  cacheMatrix$setInverse(inv)
+  inv
+}