cachematrix.R

## Put comments here that give an overall description of what your
## functions do

## This function generates a matrix that caches the inverse when it is calculated by cacheSolve.
## The function is called with an invertible matrix m as argument
## For a cached matrix x, use x$get() to retrieve the matrix and x$set(new_matrix) to change the values
## Other functions are helper functions for cacheSolve.

makeCacheMatrix <- function(x = matrix()) {
  i <- NULL
  set <- function(y) {
    x <<- y
    i <<- NULL
  }
  get <- function() x
  setinv <- function(inv) i <<- inv
  getinv <- function() i
  list(set = set, get = get, setinv = setinv, getinv = getinv)
}

## This function calculates or retrieves the inverse of a cached matrix. 
## The argument of the function is a cached matrix x generated by makeCacheMatrix(input_matrix)
## cacheSolve(x) returns the inverse of input_matrix

cacheSolve <- function(x, ...) {
  i <- x$getinv()
  if(!is.null(i)){
    message("getting cached data")
    return(i)
  }
  mat <- x$get()
  i <- solve(mat)
  x$setinv(i)
  i
}