From 5e811f5f8ffe81acdb7eb1b43b502f4381f9181c Mon Sep 17 00:00:00 2001
From: gxdlarson <gxdlarson@gmail.com>
Date: Mon, 21 Apr 2014 17:33:16 -0400
Subject: [PATCH] updated functions for peer review

---
 cachematrix.R | 69 ++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 63 insertions(+), 6 deletions(-)

diff --git a/cachematrix.R b/cachematrix.R
index a50be65aa44..0b2583cc962 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,15 +1,72 @@
-## Put comments here that give an overall description of what your
-## functions do
+## the purpose of the following two functions is to create a
+## special object that stores a numeric matrix and cache's its
+## inverse matrix.  the inverse matrix is cached in the sense
+## that it can be computed once and then stored for further use.
 
-## Write a short comment describing this function
+## the makeCacheMatrix() function will create
+## a list object with four (4) functions. these
+## functions consist of setters and getters for
+## the matrix 'x' and its inverse 'm'.
+## note: both 'x' and 'm' are defined in
+## the makeCacheMatrix() environment and are
+## not local to any of the setters and/or getters.
 
 makeCacheMatrix <- function(x = matrix()) {
-
+    m <- NULL
+    
+    ## setter function to initialize or change
+    ## the matrix 'x' and set the inverse matrix
+    ## 'm' to null.
+    set <- function(y) {
+        ## perhaps there should be a check to see
+        ## whether x and y are equal before doing
+        ## the following assignments. oh well ...
+        x <<- y
+        m <<- NULL
+    }
+    
+    ## getter function to retrieve the matrix 'x'
+    get <- function() x
+    
+    ## setter function to set inverse matrix 'm' to
+    ## value supplied with inverse parameter.
+    ## this function should only be called from the
+    ## cacheSolve() function.  otherwise, there is
+    ## no guarantee the inverse matrix here is valid.
+    setinverse <- function(inverse) m <<- inverse
+    
+    ## getter function to get the inverse matrix 'm'
+    getinverse <- function() m
+    
+    ## function declarations for list items.
+    ## enables the use of x$<item> syntax
+    list(set = set, get = get,
+         setinverse = setinverse,
+         getinverse = getinverse)
 }
 
 
-## Write a short comment describing this function
+## the cacheSolve() function  returns the inverse matrix 'm'
+## of a matrix 'x' created with the makeCacheMatrix() function.
+## if the inverse matrix 'm' is null, then this function will
+## compute the inverse matrix by calling the solve() function
+## with matrix 'x'.
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+    ## get the inverse matrix 'm' stored in 'x'
+    m <- x$getinverse()
+    
+    ## if inverse exists,
+    ## just return it.
+    if(!is.null(m)) {
+        message("getting cached data")
+        return(m)
+    }
+    
+    ## if inverse does not exist,
+    ## compute it, store it,
+    ## return it.
+    m <- solve(x$get(), ...)
+    x$setinverse(m)
+    m
 }