Added matrix caching functionality

anlag · anlag · commit 592ff3380a31 · 2015-01-25T22:28:53.000+01:00
diff --git a/cachematrix.R b/cachematrix.R
@@ -1,15 +1,51 @@
-## Put comments here that give an overall description of what your
-## functions do
-
-## Write a short comment describing this function
+## Solving for the inverse of a given (non-singular) matrix
+## Subsequent calls will use a cached value for the inverse, if available
 
+## Initialize a matrix environment with caching, define interface functions
 makeCacheMatrix <- function(x = matrix()) {
-
+    # the inverse starts out undefined
+    inverse <- NULL
+    
+    # save a new matrix
+    set <- function(y) {
+        x <<- y
+        # the inverse of a new matrix will begin undefined
+        inverse <<- NULL
+    }
+    
+    # return the currently loaded matrix
+    get <- function() x
+    
+    # save the inverse of the current matrix
+    setinv <- function(inv) inverse <<- inv
+    
+    # return the inverse
+    getinv <- function() inverse
+    
+    # when initialized, return the four subfunctions of this environment
+    list(set = set, get = get, setinv = setinv, getinv = getinv)
 }
 
-
-## Write a short comment describing this function
-
+## Takes a predefined matrix (from makeCacheMatrix) and returns its inverse
+## Will use a cached value if available, if not it will be solved for and saved
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+    # ask the matrix environment for a cached inverse
+    inverse <- x$getinv()
+    
+    # check if the inverse is cached already, if so just return it
+    if(!is.null(inverse)) {
+        message("matrix inverse found in cache! let's use it")
+        return(inverse)
+    }
+    
+    # no cached value found, solve for the inverse
+    message("matrix inverse NOT found in cache! we'll have to solve for it")
+    matrix <- x$get()
+    inverse <- solve(matrix, ...)
+    
+    # save the newly solved for inverse to the matrix environment
+    x$setinv(inverse)
+    
+    # return the inverse as requested
+    inverse
 }
