implemented Programming Assignment rdpeng#2

Author: markfisher

cachematrix.R

@@ -1,15 +1,56 @@
-## Put comments here that give an overall description of what your
-## functions do
+## The functions defined below enable the use of a wrapper for a matrix so that
+## the result of its inverse calculation can be cached. The makeCacheMatrix
+## function creates the wrapper itself, and the cacheSolve function will return
+## the inverse matrix for any such wrapper. If cacheSolve has already
+## calculated the inverse for an input and cached it, it will simply return
+## that inverse rather than recalculating. See the comments preceding the
+## makeCacheMatrix and solveCache functions for more detail.
 
-## Write a short comment describing this function
+## The makeCacheMatrix function returns a wrapped matrix so that its inverse
+## matrix can be cached after the first time it is calculated. The get and
+## set functions provide access to the wrapped matrix itself, while the
+## getinverse and setinverse provide access to the inverse matrix.
+## For example, the cacheSolve function uses those functions to check
+## whether a cached inverse exists already, and to provide the inverse
+## value to be cached after the initial calculation.
 
 makeCacheMatrix <- function(x = matrix()) {
-
+        i <- NULL
+        set <- function(y) {
+                x <<- y
+                i <<- NULL
+        }
+        get <- function() x
+        setinverse <- function(inverse) i <<- inverse
+        getinverse <- function() i
+        list(set = set,
+             get = get,
+             setinverse = setinverse,
+             getinverse = getinverse)
 }
 
 
-## Write a short comment describing this function
+## The cacheSolve function takes a cache matrix as input and returns the
+## inverse matrix. If that inverse had already been calculated for that cache
+## matrix, the cached value will be returned, avoiding any need to recalculate.
+## If the inverse had not yet been calculated for that cache matrix instance,
+## it will be calculated and returned, but also cached for any subsequent calls
+## to this function for that same cache matrix.
 
 cacheSolve <- function(x, ...) {
         ## Return a matrix that is the inverse of 'x'
+        i <- x$getinverse()
+        ## Check if the inverse is available in the cache matrix
+        if(!is.null(i)) {
+                message("returning cached inverse")
+                return(i)
+        }
+        ## The inverse is not available, need to calculate it
+        ## Get the raw matrix that is wrapped in the cache matrix
+        data <- x$get()
+        ## Calculate the inverse of the matrix
+        i <- solve(data, ...)
+        ## Set the inverse result on the cache matrix
+        x$setinverse(i)
+        i
 }