Completing assignment rdpeng#3.

cschooley · cschooley · commit 3d7da8aeaf29 · 2015-08-20T14:02:10.000-06:00
diff --git a/cachematrix.R b/cachematrix.R
@@ -1,15 +1,39 @@
-## Put comments here that give an overall description of what your
-## functions do
+## Matrix inversion is usually a costly computation and there may be some benefit to caching 
+ ##the inverse of a matrix rather than compute it repeatedly (there are also alternatives to 
+ ##matrix inversion that we will not discuss here). Your assignment is to write a pair of 
+ ##functions that cache the inverse of a matrix.
 
-## Write a short comment describing this function
+## This function creates (returns) a special "matrix" object that can cache its inverse.
 
 makeCacheMatrix <- function(x = matrix()) {
-
+  i <- NULL
+  set <- function(y) {
+    x <<- y
+    i <<- NULL
+  }
+  get <- function() x
+  setinv <- function(solve) i <<- solve
+  getinv <- function() i
+  list(set = set, get = get,
+       setinv = setinv,
+       getinv = getinv)
 }
 
 
-## Write a short comment describing this function
+##  This function computes the inverse of the special "matrix" returned by makeCacheMatrix above.
+  ## If the inverse has already been calculated (and the matrix has not changed), 
+  ## then the cachesolve should retrieve the inverse from the cache.
 
 cacheSolve <- function(x, ...) {
         ## Return a matrix that is the inverse of 'x'
+  i <- x$getinv()
+  if(!is.null(i)) {
+    message("getting cached data")
+    return(i)
+  }
+  data <- x$get()
+  i <- solve(data, ...)
+  x$setinv(i)
+  i
 }
+
