how to create nxn matrix with main diagonal that enters odd rows/columns with zero and even ones start with 2(n+1) sequence

im trying to write a code where even main diagonal entries start off with 2 and continue 4,6,8.... etc but i only get outputs of 2. im assuming my problem is with the n=n+1 counter but im not sure.

my code is = for i=1:30;

For j=1:30;

for i=j

c=1;

if mod(i,2)~0 A(i,j)=2*c c=c+1; if mod (i, 2) ==0

A(i, j)=0;

end

end

end end

end

Answer 1

[Torsten]

n=10;
A=zeros(n);
for i=2:2:n
    A(i,i) = i;
end
A

A = 10x10

0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 10

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Answer 2

[John D'Errico]

Simple is to use diag.

n = 5; % Now many non-zero elements will we have?
N = 1:(2*n); % a simple index vector
D = N.*mod(N-1,2); % create the elements of the main diagonal
A = diag(D)

A = 10x10

0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 10

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