Add makeCacheMatrix and cacheSolve functions

Author: johngraham

cachematrix.R

@@ -1,15 +1,43 @@
-## Put comments here that give an overall description of what your
-## functions do
 
-## Write a short comment describing this function
+## These functions allow for the caching of "expensive" computations like 
+## the matrix inverse.
 
-makeCacheMatrix <- function(x = matrix()) {
 
+## makeCacheMatrix takes a regular matrix and turns it into a "super matrix"
+## that stores a matrix and it's inverse result together.
+## The matrix is stored as x
+## The matrix inverse is stored as inv, set to NULL until the operation is made
+## There are 4 accessor functions to get and set the values.
+
+makeCacheMatrix <- function(x = matrix()) {
+     inv <- NULL
+     set <- function(y) {
+       x <<- y
+       inv <<- NULL
+     }
+     get <- function() x
+     setinverse <- function(inver) inv <<- inver
+     getinverse <- function() inv
+     list(set = set, get = get,
+          setinverse = setinverse,
+          getinverse = getinverse)
 }
 
 
-## Write a short comment describing this function
+## Returns inverse of matrix "x" from solve()
+## This function is very similar to cachemean example
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
-}
+        ## Return a matrix that is the inverse of 'x'  
+        inv <- x$getinverse()
+        if(!is.null(inv)) {
+          message("getting cached data")
+          return(inv)
+        }
+        
+        # and if *not* cached, compute inverse and save it
+        data <- x$get()
+        inv <- solve(data)
+        x$setinverse(inv)
+        inv
+}