Working inverse matrixfunctions and cache

gregelin · gregelin · commit db6d076c7c5f · 2015-10-25T13:25:42.000-04:00
diff --git a/cachematrix.R b/cachematrix.R
@@ -4,12 +4,46 @@
 ## Write a short comment describing this function
 
 makeCacheMatrix <- function(x = matrix()) {
-
+  # first make a local variable `im` for the inverse matrx
+  im <- NULL
+  # enable setting of global env variables
+  set <- function(y) {
+    ## scope matrix to a global env variable `x`
+    x <<- y
+    ## scope an empty global env variable `im`
+    im <<- NULL
+  }
+  ## return original matrix
+  get <- function() {x}
+  ## Set `im` to be calculated inversematrix in global environment lexical scope by using `<<-`
+  setinverse <- function(inversematrix) {
+    im <<- inversematrix 
+  }
+  # retrieve the inverse matrix of x
+  getinverse <- function() {im}
+  list(set = set, get = get, setinverse = setinverse, getinverse = getinverse)
 }
 
 
 ## Write a short comment describing this function
+## assume matrix `x` is always invertable
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
-}
+  ## Return a matrix that is the inverse of 'x'
+  # `x` is a matrix
+  # `ix` is inverse of matrix
+
+  # `x` is makeCacheMatrix object
+  ix <- x$getinverse()
+  if (!is.null(ix)) {
+    message("getting cached data")
+    return(ix)
+  }
+  
+  ## inverse the matrix
+  message("calculating inverse and caching result")
+  matrix <- x$get()
+  ix <- solve(matrix, ...)
+  x$setinverse(ix)
+  ix
+}
