[英]How to plot user-defined functions in R?
I am supposed to write a function for Stirling Numbers of the Second Kind, given by the formula: 我应该为第二类斯特林数写一个函数,由下式给出:
For this, I have written the following function in R: 为此,我在R中编写了以下函数:
stirling <- function(n, k)
{
sum = 0
for (i in 0:k)
{
sum = sum + (-1)^(k - i) * choose(k, i) * i^n
}
sum = sum / factorial(k)
return(sum)
}
The next part of the question is to "create a plot for n = 20, k = 1,2,...,10" . 问题的下一部分是“为n = 20创建一个图,k = 1,2,...,10” 。 I did some research and I think the methods
curve
or plot
might help me. 我做了一些研究,我认为方法
curve
或plot
可能对我有帮助。 However, I am guessing these methods are used when y
is of the form f(x)
(ie a single argument). 但是,我猜这些方法是在
y
为f(x)
形式时使用的(即单个参数)。 But here, I have two arguments ( n
and k
) in my function stirling
so I am not sure how to approach this. 但在这里,我有两个参数(
n
和k
)在我的功能stirling
,所以我不知道如何处理这一点。
Also, I tried converting the values of k
(0, 1, 2..., 10) to a vector and then passing them to stirling
, but stirling
won't accept vectors as input. 此外,我尝试将
k
(0,1,2 ...,10)的值转换为矢量,然后将它们传递给stirling
,但stirling
将不接受矢量作为输入。 I am not sure how to modify the code to make stirling
accept vectors. 我不知道如何修改代码以使
stirling
接受向量。
Any suggestions? 有什么建议么?
As pointed out in the comments, you can vectorize
to do this: 正如评论指出的那样,你可以
vectorize
做到这一点:
Vectorize creates a function wrapper that vectorizes the action of its argument FUN.
Vectorize创建一个函数包装器,用于向量化其参数FUN的动作。
Vectorize(FUN, vectorize.args = arg.names, SIMPLIFY = TRUE, USE.NAMES = TRUE)
(vstirling <- Vectorize(stirling))
# function (n, k)
# {
# args <- lapply(as.list(match.call())[-1L], eval, parent.frame())
# names <- if (is.null(names(args)))
# character(length(args))
# else names(args)
# dovec <- names %in% vectorize.args
# do.call("mapply", c(FUN = FUN, args[dovec], MoreArgs = list(args[!dovec]),
# SIMPLIFY = SIMPLIFY, USE.NAMES = USE.NAMES))
# }
so vstirling()
is the vectorized version of stirling()
. 所以
vstirling()
是stirling()
的矢量化版本。
vstirling(20, 1:10)
# [1] 1.000000e+00 5.242870e+05 5.806064e+08 4.523212e+10 7.492061e+11 4.306079e+12 1.114355e+13 1.517093e+13
# [9] 1.201128e+13 5.917585e+12
Now all that is left is creating a plot: 现在剩下的就是创建一个情节:
plot(x = 1:10, y = vstirling(20, 1:10), ylab = "S(20, x)", xlab = "x")
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