Silvie Sirova - Programming Assignement 2 - solution

cachematrix.R

@@ -1,15 +1,42 @@
-## Put comments here that give an overall description of what your
-## functions do
+## These 2 functions enable to calculate matrix inversion and store it
+## in cache. The purpose is to avoid repeating time consuming computation.
+## example call: mx <- makeCacheMatrix(matrix(c(2,5,1,3),nrow=2,ncol=2))
+##               cacheSolve(mx)
 
-## Write a short comment describing this function
 
-makeCacheMatrix <- function(x = matrix()) {
+## makeCacheMatrix creates an object-list based on a matrix. 
+## It can be used for catching the inverse of that matrix.
+## ! Assumption: x is always a square invertible matrix !
 
+makeCacheMatrix <- function(x = matrix()) {
+        #browser()
+        a <- NULL
+        set <- function(b = matrix()) {
+                x <<- b
+                a <<- x
+        }
+        get <- function() x
+        setinv <- function(solve) a <<- solve
+        getinv <- function() a
+        list(set = set, get = get,
+             setinv = setinv,
+             getinv = getinv)
 }
 
-
-## Write a short comment describing this function
+## cacheSolve checks if the inverse of the matrix from makeCacheMatrix has 
+## already been computed. If so and the matrix not changed, it returns 
+## the inverse from cache, otherwise it computes the inverse of the matrix 
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+        #browser()
+        a <- x$getinv()
+        if(!is.null(a)) {
+                message("getting matrix inversion from cache")
+                return(a)
+        }
+        data <- x$get()
+        a <- solve(data)
+        x$setinv(a)
+        a
 }
+