implemented makeCacheMatrix and cacheSolve for caching matrix inverse

tra · tra · commit 5448ea3a6042 · 2014-04-15T21:09:03.000-06:00
diff --git a/cachematrix.R b/cachematrix.R
@@ -1,15 +1,47 @@
-## Put comments here that give an overall description of what your
-## functions do
+## The provided functions create a matrix which knows how to
+## cache it's inverse when needed.
+## Usage:
+##  m = makeCacheMatrix(mymatrix)
+##  cacheSolve(m)  # computes and caches on the first call
+##  cacheSolve(m)  # returns cache on subsequent calls
 
-## Write a short comment describing this function
+
+## Make a version of the matrix which is used to save the cache of the inverse
 
 makeCacheMatrix <- function(x = matrix()) {
+    inverse.cache <- NULL
+    set <- function(y) {
+        x <<- y
+        inverse.cache <<- NULL
+    }
+    get <- function() x
+    setinverse <- function(inverse) inverse.cache <<- inverse
+    getinverse <- function() inverse.cache
 
+    # return the list of functions that allow the cache to be manipulated
+    list(set = set,
+         get = get,
+         setinverse = setinverse,
+         getinverse = getinverse)
+    
 }
 
 
-## Write a short comment describing this function
+## Return the cached inverse of a matrix or
+## compute and cache the inverse if not cached.
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+    # see if we have the inverse cached
+    inverse <- x$getinverse()
+    if(!is.null(inverse)) {
+        message("using cached inverse")
+    } else {
+        message("computing and caching inverse")
+        # not cached, get the matrix and invert it
+        data <- x$get()
+        inverse <- solve(data, ...)
+        # save the inverse in the cache
+        x$setinverse(inverse)
+    }
+    inverse
 }
