cachematrix.R

# makeCacheMatrix is a function that returns a list of functions
# Its puspose is to store a martix and a cached value of the inverse of the 
# matrix. Contains the following functions:
# * setMatrix      set the value of a matrix
# * getMatrix      get the value of a matrix
# * cacheInverse   get the cahced value (inverse of the matrix)
# * getInverse     get the cahced value (inverse of the matrix)
#
# Notes:
# This is a general code I have written as part of my answer.
# An example of the code shall be after this.
# makeCacheMatrix function

makeCacheMatrix <- function(x = numeric()) {
  
  # holds the cached value or NULL if nothing is cached
  # initially nothing is cached so set it to NULL
  cache <- NULL
  
  # store a matrix
  setMatrix <- function(newValue) {
    x <<- newValue
    # since the matrix is assigned a new value, flush the cache
    cache <<- NULL
  }
  
  # returns the stored matrix
  getMatrix <- function() {
    x
  }
  
  # cache the given argument 
  cacheInverse <- function(solve) {
    cache <<- solve
  }
  
  # get the cached value
  getInverse <- function() {
    cache
  }
  
  # return a list. Each named element of the list is a function
  list(setMatrix = setMatrix, getMatrix = getMatrix, cacheInverse = cacheInverse, getInverse = getInverse)
}


# The following function calculates the inverse of a "special" matrix created with 
# makeCacheMatrix
cacheSolve <- function(y, ...) {
  # get the cached value
  inverse <- y$getInverse()
  # if a cached value exists return it
  if(!is.null(inverse)) {
    message("getting cached data")
    return(inverse)
  }
  # otherwise get the matrix, caclulate the inverse and store it in
  # the cache
  data <- y$getMatrix()
  inverse <- solve(data)
  y$cacheInverse(inverse)
  
  # return the inverse
  inverse
}

#Example code.

a <- makeCacheMatrix();
summary(a);
# create a square matrix (reason `solve` only handles square matrices )
a$setMatrix( matrix(c(1,2,12,13), nrow = 2, ncol = 2) );
a$getMatrix();
cacheSolve(a)
# the 2nd time we run the function, we get the cached value
cacheSolve(a)