% Function Extracts lines from M indexed by I
function [M] = extract(M,I);    % 篩選功能
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% 從矩陣M中刪除第I行
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Maux = zeros(size(M));
Maux(I,:) = M(I,:);
M = M - Maux;
[I] = find(M(:,1)~=0);
M = M(I,:);