initial commit of cachematrix.R

Author: lstuder

cachematrix.R

@@ -1,15 +1,60 @@
 ## Put comments here that give an overall description of what your
 ## functions do
 
+# Usage:
+# > M <- matrix(c(1,2,3,4),2,2)
+# > NN <- makeCacheMatrix()
+# > NN$set(M)
+# > NN$get()
+#      [,1] [,2]
+# [1,]    1    3
+# [2,]    2    4
+# > NN$getinverse()
+# NULL
+# > cacheSolve(NN)
+#      [,1] [,2]
+# [1,]   -2  1.5
+# [2,]    1 -0.5
+# > NN$getinverse()
+#      [,1] [,2]
+# [1,]   -2  1.5
+# [2,]    1 -0.5
+# > cacheSolve(NN)
+# getting cached data
+#      [,1] [,2]
+# [1,]   -2  1.5
+# [2,]    1 -0.5
+
 ## Write a short comment describing this function
 
 makeCacheMatrix <- function(x = matrix()) {
+    inverse_matrix <- NULL
+    set <- function(y) {
+        a_matrix <<- y
+        inverse_matrix <<- NULL
 
+    }
+    get <- function() a_matrix
+    setinverse <-  function(the_inverse_matrix) inverse_matrix <<- the_inverse_matrix
+    getinverse <- function() inverse_matrix
+    list(set = set, get = get,
+        setinverse = setinverse,
+        getinverse = getinverse)
 }
 
 
 ## Write a short comment describing this function
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
-}
+    ## Return a matrix that is the inverse of 'x'
+    ## to be precise, 'x' is a composite object built up by a call to makeCacheMatrix()
+    inverse_matrix <- x$getinverse()
+    if(!is.null(inverse_matrix)) {
+        message("getting cached data")
+        return(inverse_matrix)
+    }
+    the_matrix_elements <- x$get()
+    inverse_matrix <- solve(the_matrix_elements, ...)
+    x$setinverse(inverse_matrix)
+    inverse_matrix
+}