用matlab调用函数function Saml = Sam(data, m, r)，并输入data为[20,30,40,50],m=2,r=0.2，设置输出的Saml与data相同长度

您可以按照以下方式使用MATLAB调用函数：

1. 首先，创建一个名为“Sam.m”的新文件，并将以下代码复制粘贴到该文件中：

function Saml = Sam(data, m, r)
% This function calculates the sample mean of the input data and returns a
% vector of the same length as the input data with each element set to the
% sample mean.
%
% Inputs:
%   data - input data (a vector)
%   m - number of samples to take
%   r - sampling rate (i.e., the proportion of data to include in each sample)
%
% Output:
%   Saml - vector of sample means (same length as input data)

n = length(data); % determine length of input data

Saml = zeros(1,n); % initialize output vector to zeros

for i = 1:n % loop over each element of the input data
    samples = zeros(1,m); % initialize vector to store samples
    for j = 1:m % loop over each sample
        idx = randperm(n,floor(r*n)); % randomly select indices for the sample
        samples(j) = mean(data(idx)); % calculate the sample mean and store it
    end
    Saml(i) = mean(samples); % calculate the mean of the sample means and store it
end

2. 保存文件后，您可以在MATLAB命令窗口中输入以下命令来调用该函数并获取输出：

data = [20,30,40,50];
m = 2;
r = 0.2;
Saml = Sam(data,m,r)

这将生成一个名为“Saml”的向量，其中包含与输入数据相同长度的样本均值。