Lexical Scoping练习以及详细答案分析

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    This s an R function which is able to cache potentially time-consuming computations.

    Matrix inversion is usually a costly computation and there may be some benefit to caching the inverse of a matrix rather than compute it repeatedly (there are also alternatives to matrix inversion that we will not discuss here). Your assignment is to write a pair of functions that cache the inverse of a matrix.

（this s the Assignment from coursera “R programming" of "DATA SCIENCE"  ）

---

1.makeCacheMatrix:

This function creates a special "matrix" object that can cache its inverse.

makeCacheMatrix <- function(x=matrix(),...){
       m<-NULL
       set<-function(y){
               x<<-y #用<<-可以可以使起在赋值行为均在environment hierarchy上进行
               m<<-NULL
       }
       get<-function() x
       setM<-function(solve) m<<-solve
       getM<-function() m
       list(set=set,get=get,setM=setM,getM=getM)
}

---

2.cacheSolve:

This function computes the inverse of the special "matrix" returned by makeCacheMatrix above. If the inverse has already been calculated (and the matrix has not changed), then the cachesolve should retrieve the inverse from the cache.

#computes the inverse of the special "matrix" returned by makeCacheMatrix above. If the inverse has already been calculated (and the matrix has not changed), then the cachesolve should retrieve the inverse from the cache.
cacheSolve <- function(x, ...) {
  m <- x$getM()
  if(!is.null(m)){
    message("TO cached data")
    return(m)
  }
  data <- x$get()
  m <- solve(data,...)
  x$setM(m)
  m
  ## Return a matrix that is the inverse of 'x'
}

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