diff --git a/cachematrix.R b/cachematrix.R
index a50be65aa44..ed4f892efa2 100644
--- a/cachematrix.R
+++ b/cachematrix.R
@@ -1,15 +1,48 @@
-## Put comments here that give an overall description of what your
-## functions do
+# Matrix inverse solver with caching ability
+# Usage:
+# 1. Create an invertible matrix 'mat'
+# 2. Convert the matrix to a cached form:
+#    cache_mat <- makeCahceMatrix(mat)
+# 3. Use 'cacheSolve(cache_mat)' to obtain the inverse.
+# 4. If cacheSolve are applied to the same cache_mat,
+#    a cached copy will be returned.
 
-## Write a short comment describing this function
 
+# Create a cached matrix object as a list.
+# Input parameters: a square matrix
+# Returns: a list with follwing attributes
+# get: get function for cached matrix
+# set: set function for cached matrix
+# get_inv: get function for cached inverse
+# set_inv: set function for cached inverse
+# Initially cache_inv = NULL and x = matrix()
 makeCacheMatrix <- function(x = matrix()) {
-
+  cache_inv <- NULL
+  set <- function(y) {
+    x <<- y
+    cache_inv <<- NULL
+  }
+  get <- function() x
+  set_inv <- function(inv) cache_inv <<- inv
+  get_inv <- function() cache_inv
+  list(set=set, get=get, set_inv=set_inv, get_inv=get_inv)
 }
 
 
-## Write a short comment describing this function
-
+# Inverse solver with cache
+# Input paramter: a list created by makeCacheMatrix
+# Returns: a square matrix, inverse to the matrix stored
+#          in the input object
+# Extra parameters as in the R 'solve' function can be
+# input as well.
 cacheSolve <- function(x, ...) {
-        ## Return a matrix that is the inverse of 'x'
+  cache_inv <- x$get_inv()
+  if (!is.null(cache_inv)) {
+    message("getting cached data")
+    return(cache_inv)
+  }
+  data <- x$get()
+  cache_inv <- solve(data, ...)
+  x$set_inv(cache_inv)
+  cache_inv
 }