anfe67/programmingassignment2

Repository for Programming Assignment 2 for R Programming on Coursera

Introduction

I have used exactly the same "schema" provided in the vector mean example in the assignment instructions.

The first function (makeCacheMatrix) defines a wrapper object for a matrix, which I store internally as mat_obj. In practice it defines an "extended" matrix object.

This wrapper contains a second matrix object, which initially is set to NULL and that shall contain the inverse of mat_obj. This I have called mat_inv.

Upon creation of the initial object, mat_inv is set to NULL. It shall be only initialized the first time when a call to cacheSolve is made. Any successive call to cacheSolve shall return the cached object and no longer perform the inverse calculation.

Use of the set function cause a change to mat_obj, therefore also the cached matrix is set to NULL (mat_inv<-NULL), and therefore the next call to cacheSolve() shall have to invert the new mat_obj.

Variables of interest

• mat_obj: Our input matrix
• mat_inv: The inverted matrix, initially set to NULL

Internal functions (methods):

• get: Returns mat_obj
• set: Sets mat_obj
• setinverse: Sets mat_inv
• getinverse Returns the current value of mat_inv (can be NULL)

Usage example

The following makes a "makeCacheMatrix" object called my_threebythree_matrix (printing out the list of methods)

*    my_threebythree_matrix<-makeCacheMatrix(matrix(c(1,2,3,4,5,6,7,8,8),3,3)) 

To get the original matrix:

*    my_threebythree_matrix$get()

This shall output:

       [,1] [,2] [,3]
 [1,]    1    4    7
 [2,]    2    5    8
 [3,]    3    6    8

First time call of cacheSolve:

*    cacheSolve(my_threebythree_matrix)

Shall output:

            [,1]      [,2] [,3]
 [1,] -2.666667  3.333333   -1
 [2,]  2.666667 -4.333333    2
 [3,] -1.000000  2.000000   -1

A second call shall output:

 getting cached data
            [,1]      [,2] [,3]
 [1,] -2.666667  3.333333   -1
 [2,]  2.666667 -4.333333    2
 [3,] -1.000000  2.000000   -1