Homework 2 completed

psmyth · psmyth · commit eed409a57f48 · 2014-11-22T14:39:23.000-05:00
This should be the final revision of homework 2.
diff --git a/cachematrix.R b/cachematrix.R
@@ -1,15 +1,40 @@
-## Put comments here that give an overall description of what your
-## functions do
+## The Below functions demonstrate the principle of caching via lexical closure.
+## This can speed up program execution by avoiding recomputing values.
+## The functions below are modifications of the examples given for caching the
+## mean of a vector.
 
-## Write a short comment describing this function
 
-makeCacheMatrix <- function(x = matrix()) {
+## This function takes a matrix and returns a list containing:
+## "set" and "get" - functions to set and get the value of the matrix.
+## "setinverse" and "getinverse" - functions to comptute and retreive the inverse of the matrix
 
+makeCacheMatrix <- function(x = matrix()) {
+    m <- NULL
+    set <- function(y) {
+        x <<- y
+        m <<- NULL #defines m and sets it to NULL
+    }
+    get <- function() x
+    setinverse <- function(inverse) m <<- inverse ## sets m to the value of "inverse" in the environment where m is defined
+    getinverse <- function() m #returns m (as opposed to the uninverted x)
+    list(set = set, get = get,
+         setinverse = setinverse,
+         getinverse = getinverse)
 }
 
 
-## Write a short comment describing this function
+## This as an extension of the R "solve" function to handle a list returned
+## by makeCacheMatrix
 
 cacheSolve <- function(x, ...) {
         ## Return a matrix that is the inverse of 'x'
+    m <- x$getinverse()
+    if(!is.null(m)) { #if m is defined
+        message("getting cached data")
+        return(m)
+    }
+    mat <- x$get() #otherwise
+    m <- solve(mat, ...) #invert m
+    x$setinverse(m) #and cache the value
+    m #now return m
 }
