submission for Programming Assignement 2

ogopogoapps · ogopogoapps · commit 0ca252b90722 · 2014-12-15T21:44:10.000-06:00
diff --git a/cachematrix.R b/cachematrix.R
@@ -1,15 +1,85 @@
-## Put comments here that give an overall description of what your
-## functions do
+#
+# Matrix inversion is usually a costly computation.
 
-## Write a short comment describing this function
+# There may be some benefit to caching the inverse of a
+# matrix rather than compute it repeatedly. The functions
+# below implement a simple way to speed up matrix inversion
+# by caching results of previous matrix inversion in memory,
+# and retrieving the cached inversion results.
+#
+## Example
+## > x = rbind(c(1, -1/2), c(-1/2, 1))
+## > m = makeCacheMatrix(x)
 
-makeCacheMatrix <- function(x = matrix()) {
+## No cache in the first run
+## > cacheSolve(m)
+## [,1]      [,2]
+## [1,] 1.3333333 0.6666667
+## [2,] 0.6666667 1.3333333
 
-}
 
+## Retrieving from the cache in the second run
+## > cacheSolve(m)
+## getting cached data.
+## [,1]      [,2]
+## [1,] 1.3333333 0.6666667
+## [2,] 0.6666667 1.3333333
+## 
+
+# makeCacheMatrix creates a list containing a function to 
+# cache the inverse of a matrix in a cache environment
+#
+# 1. set the value of the matrix
+# 2. get the value of the matrix
+# 3. set the value of inverse of the matrix
+# 4. get the value of inverse of the matrix
+#
+makeCacheMatrix <- function(x = matrix()) {
+  inv <- NULL
+  
+  set <- function(y) {
+    x <<- y
+    inv <<- NULL
+  }
+  
+  get <- function() x
+  
+  setinverse <- function(inverse)
+    { inv <<- inverse }
+  
+  getinverse <- function() 
+    { inv }
+  
+  list(set=set, get=get,
+       setinverse=setinverse,
+       getinverse=getinverse)
+}
 
-## Write a short comment describing this function
+# cacheSolve(matrix)
+#
+# The cacheSolve function returns the inverse of the matrix.
+# cacheSolve first attempts to get the inverse of the matrix
+# from cache (using the getinverse accessor). If the inverse
+# exist in memory, then it is returned. If not, cacheSolve 
+# performs the inversion, caches the result and returns an
+# inverted matrix.
+#
+# This function assumes that the matrix is always invertible.x
+#
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
-}
+    
+  inv <- x$getinverse()
+       
+    if(!is.null(inv)) {
+      message("getting cached data.")
+      return(inv)
+    }
+    
+    data <- x$get()
+    inv <- solve(data)
+    x$setinverse(inv)
+    inv
+  }
+  
+  
