R编程：缓存矩阵的逆 [英] R programming: cache the inverse of a matrix

问题描述

我正在修读Coursera上的数据科学课程，并且对一个作业必须在其中求逆矩阵然后将其缓存的问题提出疑问。

I am following a Data Science course on Coursera and I have a question regarding one of the assignments where I have to inverse a Matrix and then cache that result.

基本上，我一直在搜索，找到了答案，但是答案的某些部分我还不了解。因此，我不想提交作业，因为我不想提交我不完全理解的任何内容。

Basically I have been googling away and I found the answer but there are parts of the answer that I do not yet understand. For this reason I don't want to submit my assignment yet since I don't want to submit anything that I do not fully understand.

我不喜欢的部分从下面的代码可以理解，其中定义了setInverse的部分。 函数（逆）inv从何而来？

The part that I do not understand from the code below is the part where setInverse is defined. where does the 'function(inverse) inv' come from? especially the 'inverse' was never defined?

在此之后返回的列表对我来说也没有太大意义？

After this a list is returned which does not make much sense to me as well?

如果有人可以花时间向我解释此功能，我将不胜感激！

If someone could take the time to explain this function to me I would be very grateful!

    makeCacheMatrix <- function(x = matrix()) {
    inv <- NULL
    set <- function(y) {
        x <<- y
        inv <<- NULL
    }
    get <- function() x
    setInverse <- function(inverse) inv <<- inverse
    getInverse <- function() inv
    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'
    inv <- x$getInverse()
    if (!is.null(inv)) {
        message("getting cached data")
        return(inv)
    }
    mat <- x$get()
    inv <- solve(mat, ...)
    x$setInverse(inv)
    inv
}

推荐答案

我不知道您的确切分配，但我会稍微更改您的函数：

I don't know your exact assignment, but I would change your function slightly:

makeCacheMatrix <- function(x = matrix()) {
  inv <- NULL
  set <- function(y) {
    x <<- y
    inv <<- NULL
  }
  get <- function() x
  setInverse <- function() inv <<- solve(x) #calculate the inverse
  getInverse <- function() inv
  list(set = set,
       get = get,
       setInverse = setInverse,
       getInverse = getInverse)
}

然后可以像这样使用它：

You can then use it like this:

funs <- makeCacheMatrix()
funs$set(matrix(1:4, 2))
funs$get()
#     [,1] [,2]
#[1,]    1    3
#[2,]    2    4
funs$setInverse()
funs$getInverse()
#     [,1] [,2]
#[1,]   -2  1.5
#[2,]    1 -0.5

该练习可能旨在教您闭包。关键是 x 和 inv 存储在集合的封闭环境中， get ， setInverse ， getInverse 功能。这意味着定义它们的环境，即 makeCacheMatrix（）调用创建的环境。看到这个：

The exercise is probably intended to teach you closures. The point is that x and inv are stored in the enclosing environment of the set, get, setInverse, getInverse functions. That means the environment within which they were defined, i.e., the environment created by the makeCacheMatrix() call. See this:

ls(environment(funs$set))
#[1] "get"        "getInverse" "inv"        "set"        "setInverse" "x"

您不仅看到四个函数在这种环境中，还包括 x 和 inv 对象（使用< <-）。而 get 和 getInverse 函数仅从其封闭环境中获取它们。

As you see not only are the four functions in this environment, but also the x and inv objects (a consequence of using <<-). And the get and getInverse functions only fetch these from their enclosing environment.

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