More effcient way to generate unit vector multiples (no for loop)?

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Hi, I am trying to generate unit vectors of N dimensions, and all the multiples of these unit vectors out to some distance, d. I want to return both the positive and negative directions. The only way I can do this so far is with the for loop below, which gets slow for large d. Order of vectors in final matrix is unimportant. Any tips would be greatly appreciated.

        tic;
        d=1e5;
        N=25;
        unit_vecs=zeros(2*N*d,N); %pre-allocation
        I=speye(N);
        for i=1:d
            unit_vecs(((i-1)*2*N+1):(i*2*N),:)=cat(1,i*I,-i*I);
        end
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