Write a function called spiral_diag_sum that takes an odd positive integer n as an input and computes the sum of all the elements in the two diagonals of the n-by-n spiral matrix. For example, starting with the number 1 and moving to the right in a c

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Govind Sankar Madhavan Pillai Ramachandran Nair 2018-10-7

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/422641-write-a-function-called-spiral_diag_sum-that-takes-an-odd-positive-integer-n-as-an-input-and-compute

编辑： James Tursa 2019-2-7

Hi, I am trying to attempt this question. But my problem is where is the spiral MATRIX.How do we compute the sum without the MATRIX.

function spiralsum = spiral_diag_sum(n)
spiralsum = 0; 
for i = 1:n 
    for j = 1:n 
        if(i==j) 
            spiralsum = spiralsum + M(i,j);
        end
    end
end
spiralsum = spiralsum + sum(M(n*n:-(n-1):1)) - M(1,1) - M(n,n)-M((floor(n/2))+1,(floor(n/2))+1) 
end

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Answer 1

RAMAKANT SHAKYA 2019-2-7

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https://ww2.mathworks.cn/matlabcentral/answers/422641-write-a-function-called-spiral_diag_sum-that-takes-an-odd-positive-integer-n-as-an-input-and-compute#answer_360022

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function sd=spiral_diag_sum(n)
s1=0;
s2=0;
a=spiral(n);
for r=1:n       %for below the diagonal elements
    
    s1=s1+sum(a(r,r));
end
a=flip(a); %flip the matrix daigonally
for s=1:n   % elements above the daigonal but the come to below after flip
    s2=s2+sum(a(s,s));
end
sd=s1 + s2-a((n+1)/2,(n+1)/2);      % element which come two times i.e. cen
end