A DUAL ALGORITHM OF PIECEWISE LINEAR PROGRAMMING WITH SUCCESSIVELY INCREASING SLOPES

A fast dual algorithm is presented for the piecewise linear programming with successively increasing slopes. The concept of the pointer is used to derive the optimality and the feasibility conditions based on the dual simplex principle, which avoids enlarging the scale of the problem due to introducing piecewise variables so that storage and calculating requirements are reduced. Finally,the example is given to demonstrate the effectiveness of the presented algorithm.     

An EOQ Model at Random when Average Demand Is a Linear Increasing Function

For certain types of inventory, the ordering cycle and demand may be random variants, which satisfy certain types distribution. The classical EOQ model usually neglects the fact. Based on the constant demand, under the hypothesis that the ordering cycle is a random variant which satisfies exponent distribution, average demand is a linear increasing function, this paper considers the effects of the time-value of capital and inflation on replenishment strategy of inventory system. Loosening the condition of basic economic order quantity model under deterministic state, the total cost function of the model is provided. The optimum order quantity and cycle are obtained. The application range of EOQ model under the constant demand is widened. The theoretical evidence is provided for the inventory system to make management decision.     

The Convergence Rates of Improveed Kernel Estimators for Regression Function

The kernel function of kernel estimator for regression function is often defined with compact support, the moment of Y is bigger than one. The convergence rate of the improved kernel estimator is discussed under the improved kernel function. The result is also discussed under random censorship. The class of applicable kernels include those having unbounded support and even not integral .The condition of moment of Y is discarded under the improved kernel estimator. The results are wholly the same as usual and generalize the relative results of the paper .     

EXISTENCE OF A BASIC OPTIMAL SOLUTION FOR LINEAR VECTOR EXTREME VALUE PROBBEM

In this paper, the concept of basic for linear vector extreme value problem is introduced in the partially ordered vector space. Some properties and results of the linear programming are generalized. And the existaence therom of basic optimal solution is proved.     

Effects of silvopastoral areas on milk production at dual-purpose cattle farms at the semi-humid old agricultural frontier in central Nicaragua

In extensive cattle production systems, the composition of grazing areas may significantly influence productivity. In dual-purpose cattle production systems in the lowland tropics, pasture lands with trees, so-called silvopastoral areas, are considered as being important, particularly to facilitate the management of crossbred European native cattle. The aim of the study was to quantify the effects of silvopastoral areas on production at dual-purpose cattle farms in the semi-humid lowlands of central Nicaragua. The relationships between seasonal milk production and herd data, and the proportions of land use types were examined for 74 farms by stepwise regression analysis.     

Surface drainage requirement of crops: Application of a piecewise linear model for evaluating submergence tolerance

Crop tolerance to land submergence is an important criterion for designing a surface drainage system for agricultural lands. This paper collates the available data from various places in India related to the studies on the submergence tolerance of crops. The paper hypothesizes that a piecewise linear model could be used to describe crop response to land submergence. According to this hypothesis, there would be no yield decline for a few initial days of submergence. If submergence continues beyond this period then there would be linear decline in yield. The unknown parameters in the model are: optimum yield, threshold time and the slope which represents the per cent yield reduction per day of additional submergence beyond the threshold.Data in respect of wheat, pigeon peas, cowpeas, pearlmillet, maize and groundnuts indicate that the model describes the data well, although in many cases the threshold is 0.0. The yield reduction varies from 5.3 to 23.2% for each day of submergence beyond the threshold. It appears that to allow for more than 1–2 days of submergence will result in more than 10% reducation in yield of dryfoot crops. For the maize crop, the seedling stage is the most sensitive stage followed by the silking stage. The grain formation stage is the least sensitive, although even at this stage the threshold is 0.0 and yield reduction is 9.3% for each day of submergence beyond the threshold. The data for 9 test crops from Texas and Venezuela were well described by the model. It is concluded that the piecewise linear model is a useful tool for describing submergence tolerance of crops and for working out surface drainage requirements for a given level of yield reduction. Frequency analysis of the daily rainfall data from some selected locations indicates that there is every likelihood of submergence at most of the stations. It is suggested that there is an urgent need for developing wet farming techniques analogous to dry farming techniques.     

组合预测方法及其在粮食产量预测中的应用

提出了一种组合预测方法，以“预测偏差绝对值的和最小”为标准，用线性规划确定组合权系数的最优加权算法，对青海省的粮食总产量进行了预测分析。结果表明，此模型具有较高的精度。     

分析阶梯流量井流试验数据的线性回归法

文中应用线性回归法，对一次阶梯流量井流试验数据进行适当交换后，可得回归直线方程，与目前采用的多次阶梯流量井流试验数据的分析相比较，在同样可以得到井流实验欲求的井损系数C，综合参数和含水层导水系数T三个参数的情况下，至少可以使抽水量的变化次数减少两次。实际算例表明，一次阶梯流量井流与多次阶梯流量法的计算结果非常吻合。     

Conversion to organic arable farming in The Netherlands: A dynamic linear programming analysis

Several studies show that organic farming is more profitable than conventional farming. However, in reality not many farmers convert to organic farming. Policy makers and farmers do not have clear insight into factors which hamper or stimulate the conversion to organic farming. The objective of this paper is to develop a dynamic linear programming model to analyse the effects of different limiting factors on the conversion process of farms over time. The model is developed for a typical arable farm in The Netherlands central clay region, and is based on two static liner programming models (conventional and organic). The objective of the model is to maximise the net present value over a 10-year planning horizon. The results of the analysis of a basic scenario show that conversion to organic farming is more profitable than staying conventional. In order to arrive at the actual profitable phase of organic farming, the farmer has to pass through the economically difficult 2-year conversion period. Sensitivity analysis shows that if depreciation is 25% higher than conventional fixed costs due to machinery made superfluous by conversion, conversion is less profitable than staying conventional. Also the availability of hired labour, which can be constrained in peak periods, has a strong effect on the cropping plan and the amount of area converted. Further analysis shows that a slight drop (2%) in organic prices lowers the labour income of the farmer and makes conversion less profitable than conventional farming. For farmers, a minimum labour income can be required to ‘survive’. The analysis shows that constraint on minimum labour income makes stepwise conversion the best way for farmers to overcome economic difficulties during conversion.     

多元线性回归和神经网络在水库调度中的应用比较研究

采用多元线性回归和改进人工神经网络算法分别建立水库多目标调度函数，并进行实例计算验证。通过比较分析，表明人工神经网络的非线性映射能力能够更好地反映水库调度中多个自变量和因变量之间的复杂关系，具有较高的模拟精度和较好的可行性，且应用简便。