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Unsteady non-Newtonian fluid flow with heat transfer and Tresca’s friction boundary conditions 非定常非牛顿流体传热与Tresca摩擦边界条件
Pub Date : 2022-01-24 DOI: 10.1186/s13663-022-00714-x
Paoli, Laetitia
We consider an unsteady non-isothermal flow problem for a general class of non-Newtonian fluids. More precisely the stress tensor follows a power law of parameter p, namely $sigma = 2 mu ( theta , upsilon , | D(upsilon ) |) |D( upsilon ) |^{p-2} D(upsilon ) - pi mathrm{Id}$ where θ is the temperature, π is the pressure, υ is the velocity, and $D(upsilon )$ is the strain rate tensor of the fluid. The problem is then described by a non-stationary p-Laplacian Stokes system coupled to an $L^{1}$ -parabolic equation describing thermal effects in the fluid. We also assume that the velocity field satisfies non-standard threshold slip-adhesion boundary conditions reminiscent of Tresca’s friction law for solids. First, we consider an approximate problem $(P_{delta })$ , where the $L^{1}$ coupling term in the heat equation is replaced by a bounded one depending on a small parameter $0 < delta ll 1$ , and we establish the existence of a solution to $(P_{delta })$ by using a fixed point technique. Then we prove the convergence of the approximate solutions to a solution to our original fluid flow/heat transfer problem as δ tends to zero.
考虑一类非牛顿流体的非等温非定常流动问题。更准确地说,应力张量遵循参数p的幂定律,即$sigma = 2 mu ( theta , upsilon , | D(upsilon ) |) |D( upsilon ) |^{p-2} D(upsilon ) - pi mathrm{Id}$,其中θ是温度,π是压力,υ是速度,$D(upsilon )$是流体的应变速率张量。然后用非平稳p- laplace Stokes系统与描述流体热效应的$L^{1}$ -抛物方程耦合来描述该问题。我们还假设速度场满足非标准阈值滑移-粘附边界条件,使人想起固体的Tresca摩擦定律。首先,我们考虑一个近似问题$(P_{delta })$,其中热量方程中的$L^{1}$耦合项被依赖于一个小参数$0 < delta ll 1$的有界项所取代,并且我们通过使用不动点技术建立了$(P_{delta })$解的存在性。然后,我们证明了原始流体流动/传热问题的近似解在δ趋于零时的收敛性。
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引用次数: 0
Numerical analysis of doubly-history dependent variational inequalities in contact mechanics 接触力学中双历史相关变分不等式的数值分析
Pub Date : 2021-12-13 DOI: 10.1186/s13663-021-00710-7
Xu, Wei, Wang, Cheng, He, Mingyan, Chen, Wenbin, Han, Weimin, Huang, Ziping
This paper is devoted to numerical analysis of doubly-history dependent variational inequalities in contact mechanics. A fully discrete method is introduced for the variational inequalities, in which the doubly-history dependent operator is approximated by repeated left endpoint rule and the spatial variable is approximated by the linear element method. An optimal order error estimate is derived under appropriate solution regularities, and numerical examples illustrate the convergence orders of the method.
本文对接触力学中的双历史相关变分不等式进行了数值分析。介绍了一种完全离散的变分不等式逼近方法,其中双历史相关算子用重复左端点规则逼近,空间变量用线性元法逼近。在适当的求解规则下,给出了最优阶误差估计,并通过数值算例说明了该方法的收敛阶数。
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引用次数: 3
Market equilibria and money 市场均衡和货币
Pub Date : 2021-11-15 DOI: 10.1186/s13663-021-00705-4
Flåm, Sjur Didrik
By the first welfare theorem, competitive market equilibria belong to the core and hence are Pareto optimal. Letting money be a commodity, this paper turns these two inclusions around. More precisely, by generalizing the second welfare theorem we show that the said solutions may coincide as a common fixed point for one and the same system. Mathematical arguments invoke conjugation, convolution, and generalized gradients. Convexity is merely needed via subdifferentiablity of aggregate “cost”, and at one point only. Economic arguments hinge on idealized market mechanisms. Construed as algorithms, each stops, and a steady state prevails if and only if price-taking markets clear and value added is nil.
根据福利第一定理,竞争市场均衡属于核心均衡,因此是帕累托最优均衡。让货币成为一种商品,这篇文章将这两个内容反过来。更准确地说,通过推广第二福利定理,我们证明了上述解可以重合为同一系统的公共不动点。数学参数调用共轭、卷积和广义梯度。凸性只需要通过总“成本”的次可微性,并且只需要在一点上。经济论点取决于理想化的市场机制。作为一种算法,当且仅当定价市场清晰且附加值为零时,每一种算法都会停止,稳定状态占据主导地位。
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引用次数: 2
Asymptotic behavior of Newton-like inertial dynamics involving the sum of potential and nonpotential terms 涉及势项和非势项和的类牛顿惯性动力学的渐近行为
Pub Date : 2021-10-18 DOI: 10.1186/s13663-021-00702-7
Adly, Samir, Attouch, Hedy, Vo, Van Nam
In a Hilbert space $mathcal{H}$ , we study a dynamic inertial Newton method which aims to solve additively structured monotone equations involving the sum of potential and nonpotential terms. Precisely, we are looking for the zeros of an operator $A= nabla f +B $ , where ∇f is the gradient of a continuously differentiable convex function f and B is a nonpotential monotone and cocoercive operator. Besides a viscous friction term, the dynamic involves geometric damping terms which are controlled respectively by the Hessian of the potential f and by a Newton-type correction term attached to B. Based on a fixed point argument, we show the well-posedness of the Cauchy problem. Then we show the weak convergence as $tto +infty $ of the generated trajectories towards the zeros of $nabla f +B$ . The convergence analysis is based on the appropriate setting of the viscous and geometric damping parameters. The introduction of these geometric dampings makes it possible to control and attenuate the known oscillations for the viscous damping of inertial methods. Rewriting the second-order evolution equation as a first-order dynamical system enables us to extend the convergence analysis to nonsmooth convex potentials. These results open the door to the design of new first-order accelerated algorithms in optimization taking into account the specific properties of potential and nonpotential terms. The proofs and techniques are original and differ from the classical ones due to the presence of the nonpotential term.
在Hilbert空间$mathcal{H}$中,我们研究了一种动态惯性牛顿法,其目的是求解包含势项和非势项和的加性结构单调方程。确切地说,我们正在寻找一个算子$A= nabla f +B $的零点,其中∇f是一个连续可微凸函数f的梯度,而B是一个非势单调和coercive算子。除了粘性摩擦项外,动力学还涉及几何阻尼项,它们分别由势f的Hessian和附加在b上的牛顿型修正项控制。基于不动点论证,我们证明了柯西问题的适定性。然后我们将生成的轨迹向$nabla f +B$零点的弱收敛性表示为$tto +infty $。收敛分析是建立在适当设置粘性和几何阻尼参数的基础上的。这些几何阻尼的引入使得控制和衰减已知的惯性方法的粘性阻尼振荡成为可能。将二阶演化方程改写为一阶动力系统,使我们能够将收敛分析扩展到非光滑凸势。这些结果为考虑势项和非势项的特定性质的一阶优化加速算法的设计打开了大门。由于非势项的存在,证明和技术是原创的,与经典的证明和技术不同。
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引用次数: 5
An adaptive splitting algorithm for the sum of two generalized monotone operators and one cocoercive operator 两个广义单调算子和一个正则算子和的自适应分割算法
Pub Date : 2021-10-04 DOI: 10.1186/s13663-021-00701-8
Dao, Minh N., Phan, Hung M.
Splitting algorithms for finding a zero of sum of operators often involve multiple steps which are referred to as forward or backward steps. Forward steps are the explicit use of the operators and backward steps involve the operators implicitly via their resolvents. In this paper, we study an adaptive splitting algorithm for finding a zero of the sum of three operators. We assume that two of the operators are generalized monotone and their resolvents are computable, while the other operator is cocoercive but its resolvent is missing or costly to compute. Our splitting algorithm adapts new parameters to the generalized monotonicity of the operators and, at the same time, combines appropriate forward and backward steps to guarantee convergence to a solution of the problem.
求运算符和零的分割算法通常涉及多个步骤,这些步骤被称为向前或向后步骤。向前的步骤是显式地使用操作符,向后的步骤通过它们的解析隐式地涉及操作符。本文研究了一种求三个算子和的零的自适应分割算法。我们假设其中两个算子是广义单调的,它们的解是可计算的,而另一个算子是广义单调的,但它的解是缺失的或计算成本高的。我们的分裂算法根据算子的广义单调性采用新的参数,同时结合适当的向前和向后步,保证问题的收敛性。
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引用次数: 3
A generalized multivariable Newton method 广义多变量牛顿法
Pub Date : 2021-09-20 DOI: 10.1186/s13663-021-00700-9
Burachik, Regina S., Caldwell, Bethany I., Kaya, C. Yalçın
It is well known that the Newton method may not converge when the initial guess does not belong to a specific quadratic convergence region. We propose a family of new variants of the Newton method with the potential advantage of having a larger convergence region as well as more desirable properties near a solution. We prove quadratic convergence of the new family, and provide specific bounds for the asymptotic error constant. We illustrate the advantages of the new methods by means of test problems, including two and six variable polynomial systems, as well as a challenging signal processing example. We present a numerical experimental methodology which uses a large number of randomized initial guesses for a number of methods from the new family, in turn providing advice as to which of the methods employed is preferable to use in a particular search domain.
众所周知,当初始猜想不属于特定的二次收敛区域时,牛顿法可能不收敛。我们提出了一系列牛顿方法的新变体,它们具有更大的收敛区域以及更理想的解附近性质的潜在优势。我们证明了新族的二次收敛性,并给出了渐近误差常数的特定界。我们通过测试问题,包括二变量和六变量多项式系统,以及一个具有挑战性的信号处理实例来说明新方法的优点。我们提出了一种数值实验方法,该方法对新家族的许多方法使用大量随机初始猜测,进而提供关于哪种方法更适合在特定搜索领域使用的建议。
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引用次数: 1
Strongly regular points of mappings 映射的强正则点
Pub Date : 2021-09-06 DOI: 10.1186/s13663-021-00699-z
Abbasi, Malek, Théra, Michel
In this paper, we use a robust lower directional derivative and provide some sufficient conditions to ensure the strong regularity of a given mapping at a certain point. Then, we discuss the Hoffman estimation and achieve some results for the estimate of the distance to the set of solutions to a system of linear equalities. The advantage of our estimate is that it allows one to calculate the coefficient of the error bound.
本文利用鲁棒下方向导数,给出了保证给定映射在某一点上的强正则性的充分条件。然后,我们讨论了霍夫曼估计,并得到了一些估计到线性方程组解集的距离的结果。我们估计的优点是它允许计算误差界的系数。
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引用次数: 4
Convergence of proximal splitting algorithms in (operatorname{CAT}(kappa)) spaces and beyond 近端分裂算法在(operatorname{CAT}(kappa))空间及以后的收敛性
Pub Date : 2021-08-24 DOI: 10.1186/s13663-021-00698-0
Lauster, Florian, Luke, D. Russell
In the setting of $operatorname{CAT}(kappa)$ spaces, common fixed point iterations built from prox mappings (e.g. prox-prox, Krasnoselsky–Mann relaxations, nonlinear projected-gradients) converge locally linearly under the assumption of linear metric subregularity. Linear metric subregularity is in any case necessary for linearly convergent fixed point sequences, so the result is tight. To show this, we develop a theory of fixed point mappings that violate the usual assumptions of nonexpansiveness and firm nonexpansiveness in p-uniformly convex spaces.
在$operatorname{CAT}(kappa)$空间中,由prox映射构建的公共不动点迭代(如prox-prox, Krasnoselsky-Mann松弛,非线性投影梯度)在线性度量子正则性的假设下局部线性收敛。对于线性收敛的不动点序列,线性度量子正则性在任何情况下都是必要的,因此结果是严密的。为了证明这一点,我们建立了一个不动点映射的理论,该理论违背了p-一致凸空间中通常的非扩张性和坚定非扩张性假设。
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引用次数: 1
Learning without loss 无损失的学习
Pub Date : 2021-07-26 DOI: 10.1186/s13663-021-00697-1
Veit Elser
We explore a new approach for training neural networks where all loss functions are replaced by hard constraints. The same approach is very successful in phase retrieval, where signals are reconstructed from magnitude constraints and general characteristics (sparsity, support, etc.). Instead of taking gradient steps, the optimizer in the constraint based approach, called relaxed–reflect–reflect (RRR), derives its steps from projections to local constraints. In neural networks one such projection makes the minimal modification to the inputs x, the associated weights w, and the pre-activation value y at each neuron, to satisfy the equation $xcdot w=y$ . These projections, along with a host of other local projections (constraining pre- and post-activations, etc.) can be partitioned into two sets such that all the projections in each set can be applied concurrently—across the network and across all data in the training batch. This partitioning into two sets is analogous to the situation in phase retrieval and the setting for which the general purpose RRR optimizer was designed. Owing to the novelty of the method, this paper also serves as a self-contained tutorial. Starting with a single-layer network that performs nonnegative matrix factorization, and concluding with a generative model comprising an autoencoder and classifier, all applications and their implementations by projections are described in complete detail. Although the new approach has the potential to extend the scope of neural networks (e.g. by defining activation not through functions but constraint sets), most of the featured models are standard to allow comparison with stochastic gradient descent.
我们探索了一种训练神经网络的新方法,其中所有损失函数都被硬约束取代。同样的方法在相位检索中非常成功,其中信号从幅度约束和一般特征(稀疏性,支持度等)重建。在基于约束的方法(称为松弛反射反射(RRR))中,优化器不采用梯度步骤,而是从对局部约束的投影中派生步骤。在神经网络中,一个这样的投影对每个神经元的输入x、相关权重w和预激活值y进行最小的修改,以满足方程$xcdot w=y$。这些预测,以及许多其他局部预测(约束前激活和后激活等)可以划分为两个集合,这样每个集合中的所有预测都可以并发地应用于整个网络和训练批中的所有数据。这种分为两组的情况类似于相位检索中的情况和设计通用RRR优化器的设置。由于该方法的新颖性,本文也可以作为一个独立的教程。从执行非负矩阵分解的单层网络开始,并以包含自编码器和分类器的生成模型结束,所有应用程序及其通过投影实现的详细描述。虽然新方法有可能扩展神经网络的范围(例如,通过约束集而不是函数来定义激活),但大多数特征模型都是标准的,以便与随机梯度下降进行比较。
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引用次数: 10
An inertial-type algorithm for approximation of solutions of Hammerstein integral inclusions in Hilbert spaces 希尔伯特空间中哈默斯坦积分结论近似解的惯性型算法
Pub Date : 2021-03-29 DOI: 10.1186/s13663-021-00691-7
A. U. Bello, M. T. Omojola, J. Yahaya
Let H be a real Hilbert space. Let $F:Hrightarrow 2^{H}$ and $K:Hrightarrow 2^{H}$ be two maximal monotone and bounded operators. Suppose the Hammerstein inclusion $0in u+KFu$ has a solution. We construct an inertial-type algorithm and show its strong convergence to a solution of the inclusion. As far as we know, this is the first inertial-type algorithm for Hammerstein inclusions in Hilbert spaces. We also give numerical examples to compare the new algorithm with some existing ones in the literature.
让 H 是一个实希尔伯特空间。让 $F:Hrightarrow 2^{H}$ 和 $K:Hrightarrow 2^{H}$ 是两个最大单调且有界的算子。假设哈默斯坦包容 $0in u+KFu$ 有一个解。我们构建了一种惯性型算法,并证明了它对包含解的强收敛性。据我们所知,这是第一个针对希尔伯特空间中哈默斯坦包容的惯性型算法。我们还给出了数值示例,将新算法与文献中的一些现有算法进行比较。
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引用次数: 0
期刊
Fixed Point Theory and Applications
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