Array Exponentials without For Loop?

Question

Alec Huynh 2021-6-17

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/858935-array-exponentials-without-for-loop

评论： Alec Huynh 2021-6-25

Hello, I hope you are doing well! I am not entirely sure how to succinctly describe the question I have, so I will instead demonstrate it.

Let's say I have two arrays:

A = [1 2 3];
B = [2 3];

I would like to do the operation A^B such that I would receive a 2D array C containing the solution of A.^B(1) and A.^B(2).

C(1,:) = A.^B(1);
C(2,:) = A.^B(2);
C = [1 4 9; 1 8 27];

I understand that I could write a For loop like this:

% Full Loop Code
A = [1 2 3];
B = [2 3];
C = zeros(length(B), length(A));
for i = 1: length(B)
    C(i, :) = A.^B(i);
end

But I am interested in knowing how to do this using only vectors and not using a For loop. When I do:

C = A.^B

I receive this error:

Error using .^

Matrix dimensions must agree.

Any suggestions? I am using MATLAB 2016b.

Thank you!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Jan 2021-6-17

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/858935-array-exponentials-without-for-loop#answer_727125

在 MATLAB Online 中打开

A = [1 2 3];
B = [2 3];
C = A .^ (B.')

4 个评论
显示 2更早的评论隐藏 2更早的评论

Jan 2021-6-18

在 MATLAB Online 中打开

@Alec Huynh: Thanks, @Steven Lord, for the explanation. An addition, why I've used .' in this case: For real arrays .' and ' produce the same result. It is a good programming practice to avoid assumptions of the inputs, so if I want to transpose the input, .' is the correct operator. Then I do not have to guess, if you (or any other use) is working with real or complex values.

This is the same strategy as e.g. specifying the dimension to operate on:

x = rand(randi(1:3, 2));  % e.g. [1,3], [2,1] or [3,2]
y = sum(x)     % ?!? critical: input might be a column or row vector
y = sum(x, 1)  % Avoid assumptions

The less assumptions the programmer includes in the code, the less likely is producing a bug or misleading output.

Alec Huynh 2021-6-25