Assignment: Caching the Inverse of a Matrix

Matrix inversion is usually a costly computation
and there may be some benefit to caching the inverse of a matrix
rather than computing it repeatedly.

Wrote a pair of functions that cache the inverse of a matrix:
 - makeCacheMatrix
 - cacheSolve
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Author: Nishi

cachematrix.R

@@ -1,15 +1,42 @@
-## Put comments here that give an overall description of what your
-## functions do
+## Assignment: Caching the Inverse of a Matrix
+## Matrix inversion is usually a costly computation
+## and there may be some benefit to caching the inverse of a matrix
+## rather than computing it repeatedly.
+## Your assignment is to write a pair of functions that cache the inverse of a matrix:
+## - makeCacheMatrix
+## - cacheSolve
 
-## Write a short comment describing this function
 
-makeCacheMatrix <- function(x = matrix()) {
+## This function creates a special "matrix" object that can cache its inverse.
 
+makeCacheMatrix <- function(x = matrix()) {
+    i <- NULL
+    set <- function(y) {
+        x <<- y
+        i <<- NULL
+    }
+    get <- function() x
+    setinverse <- function(inverse) i <<- inverse
+    getinverse <- function() i
+    list(set = set, get = get,
+         setinverse = setinverse,
+         getinverse = getinverse)
 }
 
 
-## Write a short comment describing this function
+## This function computes the inverse of the special "matrix" returned by makeCacheMatrix.
+## If the inverse has already been calculated (and the matrix has not changed),
+## then this function returns the inverse from the cache.
 
 cacheSolve <- function(x, ...) {
         ## Return a matrix that is the inverse of 'x'
+    i <- x$getinverse()
+    if(!is.null(i)) {
+        message("getting cached data")
+        return(i)
+    }
+    data <- x$get()
+    i <- solve(data, ...)
+    x$setinverse(i)
+    i
 }