solution

Author: aginiewicz

cachematrix.R

@@ -1,15 +1,51 @@
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
+## This is solution to Programming Assignment 2 of `R Programming` Coursera class
+##
+## Included function are used to cache computation of matrix inverse
+## by storing values in local environment of special cacheable matrix implementation
+##
+## Usage example:
+##
+## m <- makeCacheMatrix(matrix(1:4, nrow=2))
+## all(m$get() %*% cacheSolve(m) == diag(2)) # gives TRUE
+## all(m$get() %*% cacheSolve(m) == diag(2)) # prints "getting cached data" and returns TRUE
 
+## `makeCacheMatrix` crates cacheable matrix of out specified R matrix, or
+## when specified with no arguments it creates 1-by-1 cacheable matrix with single NA value.
+##
+## Result of this function call is "nearly object" (not S3 or S4 object),
+## implemented by list of four methods:
+##
+##  * get() - to get internal R matrix
+##  * set(matrix) - to set internal R matrix and reset earlier calculated inverse
+##  * getinv() - to get cached inverse, or NULL if no cached inverse is present
+##  * setinv(matrix) - to set cached inverse
 makeCacheMatrix <- function(x = matrix()) {
-
+        i <- NULL # we create cache variable set to NULL
+        set <- function(y) { # when we set new matrix
+                x <<- y # we replace old x with new value
+                i <<- NULL # and reset stored cache
+        }
+        get <- function() x # to get matrix, we just return x
+        setinv <- function(inv) i <<- inv # here we store inverse in cache variable
+        getinv <- function() i # and here we return it
+        list(set = set, get = get,
+             setinv = setinv,
+             getinv = getinv) # what remains is return list of functions, so we can access it from outside world
 }
 
-
-## Write a short comment describing this function
-
+## `cacheSolve` function uses `solve` function to get inverse of cacheable matrix
+## returned by `makeCacheMatrix`, but also stores the value for later use.
+## If inverse was already calculated, it will return cached result instantly.
+## This function passes excess arguments directly to solve method.
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+	inv <- x$getinv() # get cached inverse
+        if(!is.null(inv)) { # if it was calculated earlier
+                message("getting cached data")
+                return(inv) # we have it
+        } # otherise
+        m <- x$get() # we take R matrix out of cachable matrix
+        inv <- solve(m, ...) # and calculate its inverse
+        x$setinv(inv) # which we store in cachable matrix
+        inv # and return
 }
+