每行的“1”至少2个；每列的“1”刚好1个；
从而这样的矩阵必然满足：列数n至少是行数m的2倍,及2m≤n.
m = 3; %再次输入行数.
n = 7; %再次输入列数.
d = floor(n/m);
r = n - m*d;
A = zeros(m,n);
for k = 1:d
A(:,(k-1)*m+1:k*m) = eye(m);
end
A(:,d*m+1:n) = eye(m,r);