这应该能满足你的要求shuffle_vector_2_back_repetitions返回一个大小为600 x 1的向量，其中包含15个元素的单词单元数组的索引。要测试函数的正确性，请使用以下命令：

idx = shuffle_vector_2_back_repetitions;
nnz(idx(1:end-2)==idx(3:end))

它应该返回一个接近300的数字。

function out = shuffle_vector_2_back_repetitions
    out = zeros(600, 1);
    a = repmat(15, 40, 1);
    r = randi([1 15], 2, 1);
    out (1:2) = r;
    a(r(1)) = a(r(1)) - 1;
    a(r(2)) = a(r(2)) - 1;

    for k = 3:600
        if randi([0 1])
            if a(out(k-2))
                out(k) = out(k-2);
                a(out(k)) = a(out(k)) - 1;      
            else
                f = find(a);
                idx = randi(numel(f));
                out(k) = f(idx);
                a(f(idx)) = a(f(idx)) - 1;
            end
        else
            tmp = a(out(k-2));
            if tmp
                a(out(k-2)) = 0;
            end
            f = find(a);
            if isempty(f)
                f = out(k-2);
                out(k) = f;
                a(f) = tmp - 1;
                return
            end
            idx = randi(numel(f));
            out(k) = f(idx);
            a(f(idx)) = a(f(idx)) - 1;
            if tmp
                a(out(k-2)) = tmp;
            end
        end
    end
end