Programming Assignment 2. It also contains two utility functions.

Author: GetinetA

cachematrix.R

@@ -1,15 +1,117 @@
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
+## This function creates a special "matrix" object that 
+## can cache its inverse.
+## Precondition: matrix should be a square invertible matrix
+##
+## @param: a matrix object,  
+## @return: returns a list object consisting of functions
 
 makeCacheMatrix <- function(x = matrix()) {
-
+        
+    		if(!is.matrix(x) | is.null(x)){
+    		    x = matrix()
+    		}
+        
+        inverse <- NULL
+        
+        set <- function(y) {
+            if(!is.null(y) & is.matrix(y) & !NA %in% y){
+                ## update matrix only if the argument matrix isn't same as
+                ## the original matrix object, or if original matrix is empty 
+                if(!NA %in% x){
+                    if(!areMatricesEqual(x, y)){
+                        x <<- y
+                        inverse <<- NULL
+                        message("New matrix object has been set.")
+                    } 
+                } else{
+                    x <<- y
+                }
+            } else {
+                message("Argument passed is NULL, empty or isn't matrix.")
+                message("Please pass valid initialized matrix object.")
+            }
+        }
+        
+        get <- function() {x}
+        
+        setInverse <- function(inv) {
+            if(!is.null(inv) & is.matrix(inv)){
+                    inverse <<- inv
+            }
+        }
+        
+        getInverse <- function() {
+            inverse
+        }
+        
+        list(set = set, 
+             get = get,
+             setInverse = setInverse,
+             getInverse = getInverse)
 }
 
 
-## Write a short comment describing this function
+## This function computes the inverse of a special "matrix" object
+## returned by makeCacheMatrix function. If the inverse has already 
+## been calculated and the matrix has not changed, then this function 
+## retrieve the inverse from cache.The parameter is checked if it is 
+## a valid list object returned by makeCacheMatrix
+##
+## @param: a list object, that is returned by makeCacheMatrix function
+## @return: returns the mean of the special matrix object
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+      ## Return a matrix that is the inverse of 'x'
+      
+      if(isParameterValidObject(x)){
+    			invMatrix <- x$getInverse()
+    			if(!is.null(invMatrix) ) {
+    					message("getting cached data...")
+    					return(invMatrix)
+    			} 
+    			origMatrix <- x$get()
+    			if(!NA %in% origMatrix ){
+    			    message("Calculating inverse...")
+      				invMatrix <- solve(origMatrix, ...)
+      				x$setInverse(invMatrix)
+      				return(invMatrix)
+    			} else {
+    			    message("Matrix object of passed parameter is empty.")
+              message("First set matrix value using 'set' function.")
+    			}
+      } else{
+          message("Please pass a valid makeCacheMatrix object.")
+      }
+}
+
+## Utility function that checks if two matrices are equal
+## Returns true if the matrices have equal dimensions and all 
+## corresponding memeber elements are equal, otherwise false
+##
+## @param: x and y, the two matrices to be compared
+## @return: returns true if they are equal otherwise false
+
+areMatricesEqual <- function(x, y) {
+    #message("Comparing Matrix objects ...")
+    if(is.matrix(x) & is.matrix(y)){
+        if( (ncol(x) == ncol(y)) & (nrow(x) == nrow(y)) ){
+            all(x == y)
+        } 
+    }
+    else {
+        FALSE
+    }
+}
+
+## Utility function that checks if an object is a valid makeCacheMatrix object
+## That means it shoulb be a list of functions with apprpriate names
+## Returns true if it is valid object, otherwise false
+##
+## @param: param, the list object that will be validated 
+## @return: returns true if makeChacheMatrix object otherwise false
+
+isParameterValidObject <- function(param){
+    #message("Validating makeChacheMatrix object ...")
+    functionNames = c("set", "get", "setInverse", "getInverse")
+    !is.null(param) & class(param) == "list" & all(length(param)== 4) & all(names(param)==functionNames)
 }