一、總結

組合數：choose(n,k) —— 從n箇中選出k個

階乘：factorial(k) —— k!

排列數：choose(n,k) * factorial(k)

冪：^

餘數：%%

整數商：%/%

列出所有組合數矩陣：combn(x,n)

t(combn(x,n)) 轉置

二、具體例子

choose(5,3) # 10
factorial(5) # 120
choose(5,3)*factorial(3) # 60
2^10 # 1024
10 %% 3 # 1
10 %/% 3 # 3

x <- 1:5
n <-3
combn(x,n)
/*
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    1    1    1    1    1    1    2    2    2     3
[2,]    2    2    2    3    3    4    3    3    4     4
[3,]    3    4    5    4    5    5    4    5    5     5
 
*/

t(combn(x,n))
/*
      [,1] [,2] [,3]
[1,]    1    2    3
[2,]    1    2    4
[3,]    1    2    5
[4,]    1    3    4
[5,]    1    3    5
[6,]    1    4    5
[7,]    2    3    4
[8,]    2    3    5
[9,]    2    4    5
[10,]    3    4    5  
*/

END 2018-11-26 11:07:27