有限制：
\(\forall i, \sum_j A_{i,j} \times x_j \ge B_i\)
\(min \sum_j c_j \times x_j\)
对偶问题：
\(\forall j, \sum_i y_i \times A_{i,j} \le C_j\)
\(max \sum_i y_i \times B_i\)
简略证明：
∵\(B_i \le \sum_j A_{i,j} \times x_j\)，∴ \(~\sum y_i B_i \le y_i \sum_j A_{i,j} \times x_j\)
∵\(\sum A_{i,j} y_i \le c_j\), ∴ \(~\sum A_{i,j} y_i x_j\le \sum c_j x_j\)
所以\(\sum y_i B_i \le y_i \sum_j A_{i,j} \times x_j\le \sum c_j x_j\)
所以\(\sum y_iB_i \le \sum c_j x_j\)
大概可以感受到，要使\(\sum c_j x_j\)最小，\(\sum_i y_i \times B_i\)就要最大。