cachematrix.R

## The two functions in this file make it possible to create an object that
## stores a matrix and use associated functions to set and retrieve information 
## related to the matrix and its inverse.  The function cacheSolve makes it possible
## to compute and store the inverse of the matrix if the inverse has not already been
## set by the user.

## Calling makeCacheMatrix sets the matrix.  The returned object
## has the capability to set/get the matrix and set/get the matrix's inverse
makeCacheMatrix <- function(x = matrix()) {

       matrix_inverse <- NULL

       #Sets (or resets) matrix.  The matrix inverse it reset to NULL if the matrix is reset.
       set_matrix <- function(y) {
              x <<- y 
              matrix_inverse <<- NULL  #Set inverse to null if matrix is set/reset
        }

       #Retrieves matrix
       get_matrix <- function()  {
              return(x)   
       }

       #Sets the inverse of the matrix
       set_matrix_inverse <- function(inverse) {
              message("We are setting the inverse.")
              matrix_inverse <<- inverse
       }

       #Retrieves matrix inverse
       get_matrix_inverse <- function() {
              return(matrix_inverse)  
       }
 
       #This is a list of functions that can be called by the object.
       list(set_matrix=set_matrix, get_matrix=get_matrix, set_matrix_inverse=set_matrix_inverse, 
              get_matrix_inverse=get_matrix_inverse)
              
}  #closing makeCacheMatrix


## The cacheSolve function checks to see if the matrix inverse has been computed.  If so,
## it returns that value.  If not, it computes and stores the matrix's inverse
## for future use.
cacheSolve <- function(x, ...) {

       if(!is.null(x$get_matrix_inverse())) {
              message("Good news! We already have the inverse stored!")
              return(x$get_matrix_inverse()) 
       }

       matrix_inverse = solve(x$get_matrix())  #Compute matrix inverse
       x$set_matrix_inverse(matrix_inverse)    #Store matrix inverse
       return(matrix_inverse)

}  #closing cacheSolve function