Create an alternating matrix

Question

John Carroll 2022-11-30

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https://ww2.mathworks.cn/matlabcentral/answers/1867103-create-an-alternating-matrix

评论： John Carroll 2022-11-30

Hello. I am looking to create a 1xn matrix where I would enter a max value and a step size for the vector where each value alternates sign. For example I would enter a max value of 20 and a step size of 5 and the result would produce the following matrix;

[0 5 -5 10 -10 15 -15 20 -20]

Thank you in advance.

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Answer 1

DGM 2022-11-30

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https://ww2.mathworks.cn/matlabcentral/answers/1867103-create-an-alternating-matrix#answer_1115808

编辑：DGM 2022-11-30

在 MATLAB Online 中打开

There are many ways. Here's one.

% parameters
st = 5;
ev = 20;
A = [0 kron(st:st:ev,[1 -1])]
A = 1×9
     0     5    -5    10   -10    15   -15    20   -20

Here's another:

B = repmat(0:st:ev,[2 1]).*[1; -1];
B = B(2:end)
B = 1×9
     0     5    -5    10   -10    15   -15    20   -20

Here's another:

C = [0 repelem(st:st:ev,2)];
C(3:2:end) = -C(3:2:end)
C = 1×9
     0     5    -5    10   -10    15   -15    20   -20

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John Carroll 2022-11-30

This works prefectly. I was completely unaware of the kron command. Thank you.

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Answer 2

VBBV 2022-11-30

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https://ww2.mathworks.cn/matlabcentral/answers/1867103-create-an-alternating-matrix#answer_1115803

在 MATLAB Online 中打开

maxV = 20;
stepS = 5;
I = zeros(1,2*(maxV/stepS)+1);
I1 = 0:stepS:maxV;
I2 = -I1(2:end);
I(1:2:end) = I1;
I(2:2:end) = I2;
I
I = 1×9
     0    -5     5   -10    10   -15    15   -20    20