MATLAB中N个函数句柄的求和 [英] Summation of N function handles in MATLAB

问题描述

我在 MATLAB 中有 N 个函数，我可以使用 strcat、num2str 和 eval 定义它们for 循环.因此，无需手动定义，我就可以定义 N 函数.让 N=4 并让它们如下所示:

I have N functions in MATLAB and I can define them using strcat, num2str and eval in a for loop. So without defining by hand I am able to define N functions. Let N=4 and let them be given as follows:

f1=@(x) a1*x+1;
f2=@(x) a2*x+1;
f3=@(x) a3*x+1;
f4=@(x) a4*x+1;

现在我添加这四个函数，我可以手动完成如下:

Now I add these four functions and I can do this by hand as follows:

f=@(x)(f1(x)+f2(x)+f3(x)+f4(x));

这里我可以手工完成，因为我知道N=4.但是，总的来说，我永远不知道我将拥有多少功能.对于所有情况，我都无法编写新函数.

Here I can do it by hand because I know that N=4. However, in general I never know how many functions I will have. For all cases I cannot write a new function.

有没有办法自动执行此操作?我的意思是如果我给 N=6 我期待看到 MATLAB 给我这个:

Is there any way to do this automatically? I mean if I give N=6 I am expecting to see MATLAB giving me this:

f=@(x)(f1(x)+f2(x)+f3(x)+f4(x)+f5(x)+f6(x));

每当我给 N=2 然后我必须有函数 f，定义如下:

Whenever I give N=2 then I must have the function f, defined as follows:

f=@(x)(f1(x)+f2(x));

我们该怎么做?

推荐答案

首先，你应该阅读 这个答案 给出了一系列避免使用 eval 的原因.很少有 eval 是必要的，在所有其他情况下，它只会使事情复杂化.在这种情况下，您使用动态生成变量名，这被认为是一种非常糟糕的做法.正如链接的答案和该答案链接的进一步著作中所详述的那样，动态变量名称使代码更难阅读、更难维护，并且在 MATLAB 中执行速度更慢.

First of all, you should read this answer that gives a series of reasons to avoid the use of eval. There are very few occasions where eval is necessary, in all other cases it just complicates things. In this case, you use to dynamically generate variable names, which is considered a very bad practice. As detailed in the linked answer and in further writings linked in that answer, dynamic variable names make the code harder to read, harder to maintain, and slower to execute in MATLAB.

因此，与其定义函数 f1、f2、f3、... fN，做的是定义函数 f{1}, f{2}, f{3}, ... f{N}.也就是说，f 是一个元胞数组，其中每个元素都是一个匿名函数(或任何其他函数句柄).

So, instead of defining functions f1, f2, f3, ... fN, what you do is define functions f{1}, f{2}, f{3}, ... f{N}. That is, f is a cell array where each element is an anonymous function (or any other function handle).

例如，代替

f1=@(x) a1*x+1;
f2=@(x) a2*x+1;
f3=@(x) a3*x+1;
f4=@(x) a4*x+1;

你愿意

N = 4;
a = [4.5, 3.4, 7.1, 2.1];
f = cell(N,1);
for ii=1:N
   f{ii} = @(x) a(ii) * x + 1;
end

通过这些变化，我们可以轻松回答这个问题.我们现在可以编写一个函数来输出 f 中函数的总和:

With these changes, we can easily answer the question. We can now write a function that outputs the sum of the functions in f:

function y = sum_of_functions(f,x)
   y = 0;
   for ii=1:numel(f)
      y = y + f{ii}(x);
   end
end

你可以把它放在一个名为 sum_of_functions.m 的文件中，或者你可以把它放在你的函数文件或脚本文件的末尾，没关系.现在，在您的代码中，当您想计算 y = f1(x) + f2(x) + f3(x)... 时，您编写的是 y = sum_of_functions(f,x).

You can put this in a file called sum_of_functions.m, or you can put it at the end of your function file or script file, it doesn't matter. Now, in your code, when you want to evaluate y = f1(x) + f2(x) + f3(x)..., what you write is y = sum_of_functions(f,x).

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