关键词: 合作模式, 优化模型, CVaR风险度量准则, 拉格朗日函数

Abstract: According to the current central poverty alleviation policy, taking the poverty alleviation method into consideration, a new cooperative mode of order agriculture is put forward and constructs a new order agriculture optimization model is constructed. First, according to the needs of regional economic development, an agricultural cooperative is established. The farmers took part in the shares in the proportion of land area. The total land area of the cooperative is S. The cooperative obtained profits by negotiating and signing the purchase contract with the agricultural products acquisition company and used part of the profits to pay dividends to the farmers.The cooperative employs professional managers to run the business. In addition, the cooperative will provide a fixed fee,Myuan per unit area, to the farmers according to their shares to ensure their income.The types and quantities of crops planted are determined by the cooperative, which grows a variety of crops and each crop yield is Q_i (i=1,…N). At the same time, the cooperative needs to employ workers for planting. In order to improve the enthusiasm of workers, the wages of workers are positively correlated with the output of agricultural products planted. The coefficient is c_i3, that is, the total wages of workers provided by the cooperative are $\sum\limits_{i = 1}^N {{c_{i3}}{Q_i}} $. Farmers can also apply to become workers to increase their income. Here it is assumed that the number of workers in the cooperative is a, in which the number of farmers is b. The cooperative and the acquiring corporation sign contracts in accordance with the principle of "guaranteeing the purchase price and following the market". That is, the acquiring price is max(w_i^r,w_i). According to the above content, a new three-level new order agricultural supply chain optimization model of "farmers + cooperatives+acquisition companies" was constructed:
The profit function of the cooperative is:
π_e=ϕ$\sum\limits_{i = 1}^N {[{Q_i}\max (} w_i^r,{w_i}) - C({Q_i}) - {c_{i3}}{Q_i}] - MS$
The profit function of farmers is:
π_f=(1-ϕ)$\sum\limits_{i = 1}^N {[{Q_i}\max (} w_i^r,{w_i}) - C({Q_i}) - {c_{i3}}{Q_i}] + MS + \frac{{b\sum\limits_{i = 1}^N {{c_{i3}}{Q_i}} }}{a}$
Here,the C(Q_i) is the cost function.
Under the measurement criteria of conditional risk (CVaR), the specific benefits of cooperatives under different risk avoidance degrees are obtained.On the premise of ensuring the income of farmers and cooperatives, the corresponding constraint optimization model is established.Use the Lagrange function and the corresponding KKT conditions, then obtain the minimum land area that farmers can gain more benefits from joining the cooperative is
${S_1} = \frac{{\max ({w^r},w) - {c_1}}}{{2{c_2}q}}$
And the minimum fixed fee that the cooperative provide for the farmers is
$M > \frac{{q\phi (\max ({w^r},w) - {c_1})}}{2}$
In the part of case analysis, specific values are assigned to these parameters and prove the correctness of the conclusion by formula calculation. These conclusions provide a theoretical basis for the establishment of cooperatives, and also provide solutions to the low fulfillment rate in agricultural contract.

Key words: cooperation mode, optimization model, CVaR risk measurement criteria, lagrange function