Commit rdpeng#1

Author: avy

cachematrix.R

@@ -1,15 +1,55 @@
-## Put comments here that give an overall description of what your
-## functions do
+##- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+## R Programming on Coursera
+## Programming Assignment #2: Create two functions
+##
+##  (1) makeCacheMatrix
+##      This function creates a special "matrix" object that can cache its inverse.
+##      For this assignment, assume that the matrix supplied is always invertible.
+##  (2) cacheSolve: 
+##      This function computes the inverse of the special "matrix" returned by makeCacheMatrix above. 
+##      If the inverse has already been calculated (and the matrix has not changed), then cacheSolve retrieves the inverse from the cache.
+##- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
-## Write a short comment describing this function
 
-makeCacheMatrix <- function(x = matrix()) {
+## Function #1: makeCacheMatrix
+## makeCacheMatrix takes an invertible, square matrix and returns a list of four functions that:
+## (1) set the value of the matrix (2) get the value of the matrix (3) set the value of the inverse (4) get the value of the inverse
 
+makeCacheMatrix <- function(x = matrix()) {
+  if(ifelse(nrow(x) == ncol(x), ifelse(det(x) != 0, TRUE, FALSE), FALSE)) { # check if the matrix square and invertible
+    inv <- NULL
+    set <- function(y) {
+      x <<- y
+      inv <<- NULL
+    }
+    get <- function() x
+    setInverse <- function(solve) inv <<- solve
+    getInverse <- function() inv
+    list(set = set, get = get,
+         setInverse = setInverse,
+         getInverse = getInverse)
+  }
+  else { # if matrix not square and invertible, then throw an error
+    message("[makeCacheMatrix error]: 'x' must be a square, invertible matrix")
+  }
 }
 
 
-## Write a short comment describing this function
+
+
+## FUNCTION #2: cacheSolve
+## cacheSolve takes the list created by makeCacheMatrix and returns the inverse of the matrix represented in that list. 
+## If the inverse has already been calculated, cacheSolve pulls the inverse from the cache.  
+## Otherwise, cacheSolve calculates and sets the value of the inverse in the cache.
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
-}
+  inv <- x$getInverse()
+  if(!is.null(inv)) {
+    message("getting cached data")
+    return(inv)
+  }
+  data <- x$get()
+  inv <- solve(data, ...)
+  x$setInverse(inv)
+  inv
+}