Can someone explain this please?

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matmat lab 2016-11-6

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https://ww2.mathworks.cn/matlabcentral/answers/310846-can-someone-explain-this-please

评论： matmat lab 2016-11-6

I know this is from the function perms but i dont understand how it works. from this part onwards:

q = permsr(1:n-1);  % recursive calls
m = size(q,1);
P = zeros(n*m,n);
P(1:m,:) = [n*ones(m,1) q];
for i = n-1:-1:1,
   t = q;
   t(t == i) = n;
   P((n-i)*m+1:(n-i+1)*m,:) = [i*ones(m,1) t]; % assign the next m
                                               % rows in P.
end
P = V(P);
end

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Jan 2016-11-6

编辑：Jan 2016-11-6

As long as neither "permsr" nor "n" is defined, wild guessing is required to answer your question. Please post the complete code and ask a specific question. How much time should I spend to explain the meaning of "m = size(q,1)" or do I have to explain the zeros command?

matmat lab 2016-11-6

在 MATLAB Online 中打开

function P = permsr(V)
% subfunction to help with recursion
V = V(:).'; % Make sure V is a row vector
n = length(V);
if n <= 1
    P = V; 
    return; 
end
q = permsr(1:n-1);  % recursive calls
m = size(q,1);
P = zeros(n*m,n);
P(1:m,:) = [n*ones(m,1) q];
for i = n-1:-1:1,
   t = q;
   t(t == i) = n;
   P((n-i)*m+1:(n-i+1)*m,:) = [i*ones(m,1) t]; % assign the next m
                                               % rows in P.
end
P = V(P);
end

This is the full code but i dont get why is there the [n*ones(m,1) q] and like the purpose of t and q and P((n-i)*m+1:(n-i+1)*m,:) = [i*ones(m,1) t] Basically i dont understand what it is doing

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