Determine the magic sum from a magic square

Question

Farooq 2022-9-22

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https://ww2.mathworks.cn/matlabcentral/answers/1810075-determine-the-magic-sum-from-a-magic-square

评论： Nathan Hardenberg 2023-7-25

采纳的回答： Davide Masiello

Determine for a magic square of order n, the magic sum m. For example m=15 for a magic square of order 3.

For this problem I wrote:

m = sum(n)

This gave me 15 15 15. Why is this not correct?

I then tried

m = sum(n(1, :))

This gave me 15. Why is this not correct?

I don't understand why my answer is not accepted. This is for Cody Problem 1087: Magic is simple (for beginners).

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David Goodmanson 2022-9-22

Hi Farook,

It looks like you are given the size of the magic square, but not the magic square itself. So if all you are given is that the magic square is 3x3, how do you obtain 15 from n=3?

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Answer 1

Davide Masiello 2022-9-22

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https://ww2.mathworks.cn/matlabcentral/answers/1810075-determine-the-magic-sum-from-a-magic-square#answer_1058680

编辑：Davide Masiello 2022-9-22

在 MATLAB Online 中打开

I think you are inputting the magic square itself to your function, rather than its order.

I believe the relation between a magic square order (n) and the magic sum (S) is

So your function should be

function out = magic_sum(n)
out = n*(n^2+1)/2
end

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Farooq 2022-9-22

Thank you for your help!

Nathan Hardenberg 2023-7-25

在 MATLAB Online 中打开

While the formula is a valid solution I think the intended way is to sum up one colum or row, since all rows/colums and diagonals do sum up to the same number:

mag_sqr = magic(3)
mag_sqr = 3×3
     8     1     6
     3     5     7
     4     9     2
sol1 = sum(mag_sqr(:,1))  % sum up first colum
sol1 = 15
sol2 = sum(mag_sqr(1,:))  % sum up first row
sol2 = 15