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1.
我们知道,一个实二次型的标准形(或规范型)由它的秩和符号差唯一确定。一般说来,把实二次型通过满秩的线性变换化为标准形,自然能求出二次型的秩和符号差。给定一个实二次  相似文献   

2.
给出具有相同控制顶点的二次C-曲线与二次有理Bézier曲线表示同一参数曲线段的充要条件,由此得到了二次C-曲线不能精确表示双曲线段的结论;另外,还给出了二次C-曲线在任意一点的细分公式.  相似文献   

3.
大量研究表明,氯离子在混凝土中的扩散严重影响了混凝土的耐久性.基于Fick第二定律,考虑二维扩散问题,采用灵活度较好的三角形剖分单元和精确度更高的二次插值基函数,建立了氯离子在混凝土中扩散的二次有限元模型,并进行了收敛性分析.同时,对常数边界、线性边界、振荡边界的二次有限元模型进行数值模拟,有效地预测了氯离子在三种边界条件下的扩散趋势.  相似文献   

4.
本文给出了当V0 ≥ 0时 ,c′σ2 在混合模型M =( y ,Xβ ,Uξ,σ20 V0 )下的最小范数二次无偏估计的表达式及其证明 ;得到了当 y服从正态分布时 ,c′σ2 的最小范数二次无偏估计与其最小方差二次无偏估计之间的关系。  相似文献   

5.
许多抽象于实际的二次分配问题,其流矩阵与距离矩阵中有很多零元素,求解该类二次分配问题时,可通过先行利用零元素的信息减小问题规模,缩短计算时间.以二次分配问题的线性化模型为基础,提出了一种求解流矩阵与距离矩阵中同时存在大量零元素的二次分配问题新方法,不仅从理论上证明了方法的可行性,而且从实验的角度说明了该方法比以往方法更加优越.  相似文献   

6.
正定二次型判别条件的证明刘学鹏(临沂师专276005)在二次型的理论中,正定二次型是一类特殊而重要的二次型,相应的正定矩阵也是一类特殊而重要的矩阵.对于实二次型,其正定性的判别法之一,是利用其顺序主子式是否大于零.此理论根据的证明,笔者依据目前流行的...  相似文献   

7.
提出了血样的二次分组检验方法,建立了二次分组验血法预期人均检验次数最小的模型,给出了二次分组法的最佳小组人数和最佳小组数的范围,得到了求二次分组最佳方案的方法.计算结果表明模型和方法是可信的,在单个人血样呈阴性概率较大时,采用二次分组验血法能比一次分组验血法更进一步地减少检验次数,有较大的实用价值.  相似文献   

8.
研究了单输入多时滞的离散时间系统的线性二次调节问题(LQR问题),给出了求解最优控制输入序列的一种简单有效而又新颖的方法.将该动态的离散时滞系统的LQR最优控制问题最终转化成了一个静态的、不带时滞的数学规划模型——带等式线性约束的严格凸二次规划问题,并利用两种方法解这个二次规划问题,均成功地导出了系统的最优控制输入序列.仿真结果验证了我们的方法的正确有效性.  相似文献   

9.
沈伯骞 《应用数学》2002,15(4):43-46
本文给出了具有二重抛物线解的二次系统的一般形状,并与具有并重抛物线解的二次系统相比较,证明了具有二重抛物线解的二次系统也有存在极限环的可能的,而且也是唯一的,但是二重抛物线解却是不可能成为二次系统的分界线不的。  相似文献   

10.
在高等代数的实二次型内容中,正定二次型占有特殊的地位.本文从概念的回顾、正定二次型与正定矩阵的判断、二次型正定及矩阵正定的性质、其它类型二次型四个方面来设计正定二次型的习题课,并通过具体例子说明例题、习题精选的原则.  相似文献   

11.
We will try to generalize the so-called newsboy model so that we can deal with unsatisfied demand or unsold quantity. Consider the time interval that consists of multiple ordering cycles. Assume that the probability density function of demand is given for each cycle. Then our problem is to make the ordering plan with which we can maximize the expected profit. In the classical newsboy model ordering quantity is always equal to the (planned) initial inventory level. But if we take account of unsatisfied demand and unsold quantity, the (desired) ordering quantity must be determined by a proper stochastic rule. Then, in stead of determining the ordering quantity of each cycle, we must plan the initial inventory level so that the expected profit may be maximized. If unsold exists in present cycle, the ordering quantity of next cycle becomes smaller than the planned inventory level. And if unsatisfied demand exists in the present cycle, the ordering quantity of next cycle becomes larger than the planned inventory level.  相似文献   

12.
可追加订购的报童问题   总被引:7,自引:0,他引:7  
研究带有追加 (两次 )订购的报童模型 ,分析了此模型与经典 (一次订购 )报童模型的收益关系 ,服务水平评价 ,订购量与需求均值、方差、价格等的灵敏度及发现了在适当的条件下 ,最大追加订购量 M的最优解存在 ,且给出了求解的方法 .  相似文献   

13.
In this paper, we derive an optimal ordering policy for an unreliable newsboy who can place two sequential orders before the start of a single selling season by using a demand forecast update. Supply yield is modeled using a uniform distribution considering both the minimum order guarantee and the maximum yield. Our results indicate that a firm should focus on increasing the minimum order guarantee from a first stage supplier to reduce its total supply chain cost.  相似文献   

14.
闵杰  李瑶  刘斌  欧剑 《运筹与管理》2020,29(4):165-170
销售商可通过二次订货以达到降低风险、增加利润的目的,然而在实际中由于生厂商供货能力不足等不可控因素,销售商往往无法确定何时能进行第二次订货。针对这种现象,本文研究二次订货时间不确定的报童问题,假设随机订货时间点和需求率均服从均匀分布,建立了带有随机订货点的两阶段报童模型,给出了两阶段最优期望总订货量,使得零售商在整个销售期内的期望利润达到最大值。最后通过数值算例,对比分析了本文的二次订购模型与传统一次订购模型,研究结果指出在整个销售期内二次订货可以提高零售商的期望利润。  相似文献   

15.
This paper generalizes the standard newsboy model to the case including freight cost, in which the capacity of one container is the limit and the freight cost is proportional to the number of the containers used. We show that the optimal ordering quantity is either the newsboy solution or some multiple of the container’s capacity. We also propose an algorithm to compute the optimal policy. Furthermore, we generalize these results to the case in which the inventory and the price are determined jointly with emergency purchase.  相似文献   

16.
研究在资源和预算约束条件下允许外购的多产品报童问题.为解决因资源有限而引起的缺货问题,允许外购,外购的最大可得到量是给定的.建立了在非零延迟时间外购情况下以求总体花费最小值为目标函数的的优化模型,分析了模型的结构特征,结合最优化理论,利用可行方向方法对模型进行了求解.数值结果表明了模型的合理性和算法的有效性.  相似文献   

17.
A recent article in this journal employs the capital-asset pricing model for the analysis of the newsboy problem and shows how the covariance risk affects the optimal inventory policy. The purpose of this paper is to sharpen the optimality conditions given by the article and hence to provide a simple method for finding the solution. Under reasonable assumptions, this paper shows that the optimal ordering policy can be described by a single equation, regardless of the sign of the covariance term.  相似文献   

18.
企业为了稳定货源和供货关系,常与供应商签订一定时期的框架性协议。为了解决零售商在框架协议下采购报童产品的问题,本文运用强化学习建立库存决策模型并使用Q学习算法求取较优订货策略。通过生成样本随机数来模拟需求量,对比研究Q学习算法订货和传统方法订货的差别。通过多次数值实验,发现使用强化学习方法订货相比于传统订货方法(定量订货法、移动平均预测、指数平滑法)平均利润提高约7%~22%,且多次实验下强化学习方法订货相比于理想状态的平均利润相差约8%。这些发现验证了强化学习解决库存问题的有效性和可行性。本文还研究了相关参数变化对总利润的影响,发现利润随着贪婪率(ε)增加而降低、随着学习率(α)的增加而增加。该结论能够为解决相关库存问题提供新的思路。  相似文献   

19.
When an inventory item has such a limited selling period that only a single supply order can be placed to satisfy future demand, a decision-maker must determine the quantity of the order to meet future demand and how to price this stock. Although this problem has received considerable attention, related investigations typically view the demand and selling price as exogenous parameters and assume that customers cannot cancel an order or return the product after purchasing the item. Pricing is, however, an important pervasive marketing vehicle that affects demand, and customers indeed cancel or return their orders after placing them. The newsboy problem is extended here so that demand is price-dependent and customers may cancel their orders. This paper seeks to develop decision rules to maximize the total expected profit over a given planning period. Analysis results demonstrate the feasibility of applying the order-up-to structure to yield the order quantity.  相似文献   

20.
We analyze a newsboy problem with resalable returns. A single order is placed before the selling season starts. Purchased products may be returned by the customer for a full refund within a certain time interval. Returned products are resalable, provided they arrive back before the end of the season and are undamaged. Products remaining at the end of the season are salvaged. All demands not met directly are lost. We derive a simple closed-form equation that determines the optimal order quantity given the demand distribution, the probability that a sold product is returned, and all relevant revenues and costs. We illustrate its use with real data from a large catalogue/internet mail order retailer.  相似文献   

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