From 0d3fe06f460f2dddd526ed8021c39e8a694a9030 Mon Sep 17 00:00:00 2001
From: "Jeffrey A. Aborot" <jaaborot@up.edu.ph>
Date: Fri, 1 Dec 2017 17:08:46 +0800
Subject: [PATCH] Add implementation of functions makeCacheMatrix and
 cacheSolve

---
 cachematrix.R | 81 +++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 75 insertions(+), 6 deletions(-)

diff --git a/cachematrix.R b/cachematrix.R
index a50be65aa44..c363d6dbc81 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,15 +1,84 @@
-## Put comments here that give an overall description of what your
-## functions do
+## This script contains the following functions.
+# makeCacheMatrix(<invertible matrix>): 
+# This function receives as input a matrix object.
+# It then creates a composite object which has two attributes.
+# Its first attribute is a matrix object to which it
+# assigns the input matrix. Its second attribute is the
+# inverse of the input matrix which gets initialized with
+# the NULL value upon the creation of the composite object.
+# The created composite object also has member functions.
+# set() initializes the matrix object and inverse matrix object
+# attributes of the composite object. get() returns the matrix
+# object of the composite object. setsolve() sets the inverse
+# matrix attribute of the composite object into an input matrix.
+# getsolve() returns the inverse matrix attribute of the composite
+# object. The makeCacheMatrix function returns a list of its member
+# functions which are accessible via the $ operator.
+#
+# cacheSolve(<composite object output of makeCacheMatrix function>):
+# This function receives as input a composite object created using
+# the makeCacheMatrix function. This function returns the value of
+# the inverse matrix attribute of the composite matrix if is not
+# NULL. It computes for the inverse matrix attribute of the composite
+# object if the object's inverse matrix attribute is NULL and saves its
+# value which is accessible using the getsolve function.
 
-## Write a short comment describing this function
+# Note: The names of the member functions of makeCacheMatrix have been revised
+# to make them more intuitive for usage. The signature of the makeCacheMatrix
+# function has been kept the same though instructed.
 
+## Write a short comment describing this function
+# x - a matrix; assumed to be invertible
+# s - the inverse of the input matrix
 makeCacheMatrix <- function(x = matrix()) {
-
+  # initialize the inverse of the input matrix data into NULL
+  s <- NULL
+  
+  # initialize the matrix data object
+  instantiate <- function(y){
+    # initialize the matrix data into the value of the input matrix y
+    x <<- y
+    
+    # initialize the inverse of the matrix data into NULL
+    s <<- NULL
+  }
+  
+  # get the matrix data
+  getMatrix <- function() x
+  
+  # set the inverse of the matrix data
+  setInverseMatrix <- function(sol) s <<- sol
+  
+  # get the inverse of the input matrix data
+  getInverseMatrix <- function() s
+  
+  # return a list of the member functions accessible using $ operator
+  return(list(instantiate = instantiate, getMatrix = getMatrix, setInverseMatrix = setInverseMatrix, getInverseMatrix = getInverseMatrix))
 }
 
 
 ## Write a short comment describing this function
-
+# x - a matrix; assumed to be invertible
+# s - the inverse of the input matrix
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+  ## Return a matrix that is the inverse of 'x'
+  s <- x$getInverseMatrix()
+  
+  # check if the returned inverse of the input matrix x is NULL or not
+  # if the returned matrix inverse is not null, return it
+  if(!is.null(s)){
+    message("getting the inverse of matrix")
+  } else { # else if the returned inverse matrix is NULL, compute for it and return it
+    # get the matrix data of the input x 
+    data <- x$getMatrix()
+    
+    # compute for the inverse of the matrix data using solve()
+    s <- solve(data)
+    
+    # set the inverse matrix attribute of the input x to the computed inverse matrix
+    x$setInverseMatrix(s)
+  }
+  
+  # return the retrieved/computed inverse matrix
+  return(s)
 }