Implement cacheSolve

cacheSolve takes in a cache matrix x and returns the matrix's inverse.
x is a list created by the makeCacheMatrix function. If x has a
previously calculated inverse, it is used as the return value.
Otherwise, the inverse is calculated, stored in x, and returned.

Author: kinghuang

cachematrix.R

@@ -17,8 +17,20 @@ makeCacheMatrix <- function(x = matrix()) {
 }
 
 
-## Write a short comment describing this function
+## cacheSolve takes in a cache matrix x and returns the matrix's
+## inverse. x is a list created by the makeCacheMatrix function.
+## If x has a previously calculated inverse, it is used as the
+## return value. Otherwise, the inverse is calculated, stored
+## in x, and returned.
 
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+	inv <- x$getinv()
+	if (!is.null(inv)) {
+		message("getting cached data")
+		return(inv)
+	}
+	data <- x$get()
+	inv <- solve(data, ...)
+	x$setinv(inv)
+	inv
 }