From 93def9748017930a2d98611b7c47ec1dd5ead5e9 Mon Sep 17 00:00:00 2001
From: Zhenis Beisekov <zhenis.beisekov@gmail.com>
Date: Sun, 29 Sep 2019 17:18:29 +0200
Subject: [PATCH 1/3] Update cachematrix.R

Implementation of caching inverse matrix.
---
 cachematrix.R | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/cachematrix.R b/cachematrix.R
index a50be65aa44..408c9e5008a 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,15 +1,35 @@
 ## Put comments here that give an overall description of what your
 ## functions do
 
-## Write a short comment describing this function
+## makeCacheMatrix creates a list, which caches inversed matrix
 
 makeCacheMatrix <- function(x = matrix()) {
-
+    inv <- NULL
+    set <- function(y) {
+        x <<- y
+        inv <<- NULL
+    }
+    get <- function() x
+    setinv <- function(inverse) inv <<- inverse
+    getinv <- function() inv
+    list(set = set, get = get,
+         setinv = setinv,
+         getinv = getinv)
 }
 
 
-## Write a short comment describing this function
+## cacheSolve returns inverse matrix for x, which is 'cachematrix'. 
+## if there is no cached inverse matrix, it calculates new one.
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+    ## Return a matrix that is the inverse of 'x'
+    
+    m <- x$getinv()
+    if(!is.null(m)) {
+        message("getting cached data")
+        return(m)
+    }
+    inv <- solve(x$get(), diag(nrow(x$get())), ...)
+    x$setinv(inv)
+    inv
 }

From 0f8002d9a8dfd40808720a3bab2d35cbe1f109d5 Mon Sep 17 00:00:00 2001
From: Zhenis Beisekov <zhenis.beisekov@gmail.com>
Date: Mon, 30 Sep 2019 19:24:24 +0200
Subject: [PATCH 2/3] More comments to cachematrix.R

Adding more comments, so it can pass the peers' review.
---
 cachematrix.R | 32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/cachematrix.R b/cachematrix.R
index 408c9e5008a..f84a8900b28 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,17 +1,20 @@
 ## Put comments here that give an overall description of what your
 ## functions do
 
-## makeCacheMatrix creates a list, which caches inversed matrix
+## makeCacheMatrix creates an object, which keeps both
+## original matrix and inverse one. 
 
 makeCacheMatrix <- function(x = matrix()) {
-    inv <- NULL
-    set <- function(y) {
+    inv <- NULL ## variable to keep inverse matrix. 
+    ## set original matrix. Note: it does not calculate the inverse matrix
+    ## by default.
+    set <- function(y) { 
         x <<- y
         inv <<- NULL
     }
-    get <- function() x
-    setinv <- function(inverse) inv <<- inverse
-    getinv <- function() inv
+    get <- function() x ## get original matrix
+    setinv <- function(inverse) inv <<- inverse ## set inverse matrix
+    getinv <- function() inv ## get inverse matrix
     list(set = set, get = get,
          setinv = setinv,
          getinv = getinv)
@@ -25,11 +28,20 @@ cacheSolve <- function(x, ...) {
     ## Return a matrix that is the inverse of 'x'
     
     m <- x$getinv()
-    if(!is.null(m)) {
+    
+    ## check if there is the previously set value, 
+    ## because calculating inverse matrix might be expensive.
+    if(!is.null(m)) { 
         message("getting cached data")
         return(m)
     }
-    inv <- solve(x$get(), diag(nrow(x$get())), ...)
-    x$setinv(inv)
-    inv
+    
+    m <- x$get()
+    
+    ## calculate inverse matrix only if the original one is not null
+    if (!is.null(m)) {
+        m <- solve(m, ...) ## reusing m, so we can return its value
+        x$setinv(m)
+    }
+    m
 }

From 60df672d8b2611b8ea6bb13403b43d2384f85810 Mon Sep 17 00:00:00 2001
From: Zhenis Beisekov <zhenis.beisekov@gmail.com>
Date: Fri, 4 Oct 2019 13:07:24 +0200
Subject: [PATCH 3/3] Ignoring artifacts of R

---
 .gitignore | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 .gitignore

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 00000000000..ae05230ef93
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+
+.DS_Store
+.Rhistory