From d807f3e66c671656b4137ce23d457e2e502ad872 Mon Sep 17 00:00:00 2001
From: Kamil Ciemniewski <kamil@ciemniew.ski>
Date: Thu, 31 Jan 2019 19:12:05 +0100
Subject: [PATCH] Initial commit

---
 cachematrix.R | 61 +++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 54 insertions(+), 7 deletions(-)

diff --git a/cachematrix.R b/cachematrix.R
index a50be65aa44..0311d61ab92 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,15 +1,62 @@
-## Put comments here that give an overall description of what your
-## functions do
+# Constructs a smart matrix that caches its inverse.
+# The returning object is a list with 4 functions attached.
+# Each function makes use of the scoping rules present in R.
+# The underlying, "raw" matrix is held in the defining
+# environment's closure
+makeCacheMatrix <- function(x = matrix()) {
+  inv <- NULL
 
-## Write a short comment describing this function
+  set <- function(val) {
+    x <<- val
+    inv <<- NULL
+  }
 
-makeCacheMatrix <- function(x = matrix()) {
+  get <- function() x
 
-}
+  setinv <- function(val) inv <<- val
 
+  getinv <- function() inv
 
-## Write a short comment describing this function
+  list(
+    set = set,
+    get = get,
+    setinv = setinv,
+    getinv = getinv
+  )
+}
 
+# Returns an inverse of the matrix held by a "smart" matrix object
+# given by x.
+# Any additional arguments are passed to the underlying call to solve.
+# The function makes use of the interface constructed by the makeCahceMatrix
+# function in the form of the functions attached to the resulting list.
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+  inv <- x$getinv()
+
+  if(!is.null(inv)) {
+    message("getting cached data")
+    return(inv)
+  }
+
+  data <- x$get()
+
+  inv <- solve(data, ...)
+
+  x$setinv(inv)
+
+  inv
 }
+
+# TESTING:
+# -------
+# let's create an invertible matrix (as in help for ?solve) with:
+# hilbert <- function(n) { i <- 1:n; 1 / outer(i - 1, i, "+") }
+#
+# Now:
+# m <- makeCacheMatrix(hilbert(8))
+# cacheSolve(m)
+# cacheSolve(m) # again - and see the message being printed
+# m <- makeCacheMatrix(hilbert(4))
+# cacheSolve(m) # no message here again because we've changed the internal matrix
+# cacheSolve(m) # again - and see the message being printed
+