From 7657463e69c7e98e08beeafa666a401ef570f831 Mon Sep 17 00:00:00 2001
From: "Nils o. Janus" <NoJ@JanusSysteme.de>
Date: Sun, 12 Feb 2017 09:49:05 +0100
Subject: [PATCH] filled both method stubs "makeCacheMatrix" and "cacheSolve"
 with code and comments;

verified that caching works via the following timestamping test:

now <- Sys.time(); mat <- makeCacheMatrix(h10); cacheSolve(mat); diff <- Sys.time() - now; diff

now <- Sys.time(); mat$getinv(); diff <- Sys.time() - now; diff

where h10 is the 10x10 hilbert matrix
---
 cachematrix.R | 45 +++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 41 insertions(+), 4 deletions(-)

diff --git a/cachematrix.R b/cachematrix.R
index a50be65aa44..e5d0c2dafb3 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,15 +1,52 @@
-## Put comments here that give an overall description of what your
-## functions do
+## These two functions allow for caching the inverse of a matrix, to save
+## compuation time for this CPU intensive operation
+## For this, two functions are defined:
+##  - makeCacheMatrix: allows for caching a matrix and its inverse
+##  - cacheSolve: computing and storing the inverse
 
-## Write a short comment describing this function
+## allows for caching a matrix and its inverse
 
 makeCacheMatrix <- function(x = matrix()) {
+  i <- NULL
+  ## making sure that if a new matrix is set, we store its value
+  ## and reset our inverse (since we haven't calculated it yet)
+  set <- function(y) {
+    x <<- y
+    i <<- NULL
+  }
 
+  ## return the original base matrix
+  get <- function() x
+  
+  ## set new value for the inverse
+  setinv <- function(mat) i <<- mat
+  
+  ## return value of the inverse
+  getinv <- function() i
+  list(set = set, get = get, setinv = setinv, getinv = getinv)
 }
 
 
-## Write a short comment describing this function
+## This is the function to which we pass the function (which is really  a list)
+## "makeCacheMatrix" and compute and store the inverse
 
 cacheSolve <- function(x, ...) {
         ## Return a matrix that is the inverse of 'x'
+  i <- x$getinv()
+  
+  ## in case we already know the inverse, we skip recomputing it and return the cached value
+  if(!is.null(i)) {
+    message("getting cached inverse")
+    return(i)
+  }
+  
+  ## getting our base matrix ...
+  data <- x$get()
+  
+  ## ... passing it to the R solver (making sure to catch any errors) ...
+  i <- try(solve(data, ...))
+  
+  ## ... and storing and displaying the result
+  x$setinv(i)
+  i
 }