Assignment rdpeng#2

ua-umka · ua-umka · commit 6ed2784963d7 · 2014-04-21T22:03:13.000-07:00
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
+## 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.
+## Here presented a pair of functions that cache the inverse of a matrix.
 
-## Write a short comment describing this function
+## "makeCacheMatrix" function creates a special "matrix" object that can cache its inverse.
+##  This "matrix" is really a list containing a function to:
+##  set the value of the matrix
+##  get the value of the matrix
+##  set the value of the inverse matrix
+##  get the value of the inverse matrix
 
 makeCacheMatrix <- function(x = matrix()) {
-
+      inv <- NULL
+      set <- function(y) {                                             ##  set the value of the matrix
+            x <<- y
+            inv <<- NULL
+      }
+      get <- function() x                                              ##  get the value of the matrix
+      setinv <- function(solution) inv <<- solution                    ##  set the value of the inverse matrix
+      getinv <- function() inv                                         ##  get the value of the inverse matrix
+      list(set = set, get = get, setinv = setinv, getinv = getinv)     ##  return the list
 }
 
 
-## Write a short comment describing this function
+## The following function calculates the inverse matrix of the special "matrix" created with the above function.
+## However, it first checks to see if the inverse matrix has already been calculated.
+## If so, it gets the result from the cache and skips the computation.
+## Otherwise, it calculates the inverse of the matrix and sets the value in the cache via the setinv function.
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+      inv <- x$getinv()                         # query the x matrix's cache
+      if (!is.null(inv)) {                      # if there is already a value in the cache
+            message("getting cached data")
+            return(inv)                         # just return the cached value, no computation needed
+      }
+      data <- x$get()                           # if there's no value in the cache
+      inv <- solve(data, ...)                   # compute inverse matrix
+      x$setinv(inv)                             # save the result back to x's cache
+      inv                                       # return the result
 }
