cachematrix.R

## 
# written by Andy@SantaCruzIntegration.com
#
## cacheSolve()
#   returns the inverse of a makeCacheMatrix object.
#   
# side effect: will cause inv to be calculated if it does not already exist
#
# use the test() to see if code works
# If the code works you should see a matrix, all the values should be true
#

#
# makeCacheMatrix returns an object that is similar to a java POJO
# 
# To Create an object
#   myVar <- makeCacheMatrix(x)
#
# Here is an example of how to call the accessor functions stored in the objects list
#   myCM$get()
#
makeCacheMatrix <- function(x = matrix()) {
  inv <- NULL #inverse of maxtrix x
  
  # replace the matrix data member we are caching
  set <- function(y) {
    x <<- y
    inv <<- NULL
  }
  
  # return the matix pass as 'constructor' arg
  get <- function() {
    x
  }
  
  setInverse <- function(inverse) {
    inv <<- inverse
  }
  
  getInverse <- function() {
    inv
  }
  
  # This list contains all of our "member functions"
  list(set = set, get = get,
       getInverse = getInverse,
       setInverse = setInverse)
}


#
#  returns the inverse of makeCacheMatrix object
#
# checks to see if inverse value has already been stored in the makeCacheMatrix
# if not, it calculates the inverse and saves it in the makeCacheMatrix object
#  
cacheSolve <- function(x, ...) {
        ## Return a matrix that is the inverse of 'x'
        inv <- x$getInverse()
        if (!is.null(inv)) {
          message("getting cached data")
          return(m)
        }
        
        data <- x$get()
        inv <-solve(data)
        x$setInverse(inv)
        inv
}

#
# test()
# will return true if we are able to correctly calculate the inverse of a small matrix
#

test <- function() {
  m <- matrix(1:4, 2, 2)
  mcm <- makeCacheMatrix(m)
  cs <- cacheSolve(mcm)
  inv <- mcm$getInverse()
  expectedData <- list(-2, 1, 1.5, -0.5)
  expectedMatrix <- matrix(expectedData, 2, 2)
  inv == expectedMatrix
}