共查询到20条相似文献,搜索用时 93 毫秒
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用有限元方法求解双曲守恒律 总被引:1,自引:1,他引:0
分片线性插值有限元给出了求解双曲守恒律的计算方法。有别于不连续有限元方法求解双曲守恒律在相邻单元边界上求Riemann解,利用双曲守恒律的Hamilton-Jacobi方程形式,直接应用有限元求解,在CFL下,证明了计算格式满足极大值原理,并且是TVD格式。数值例子在文后给出。此外,方法推广到流体力学方程组和高维问题,将在另文中邓以讨论。 相似文献
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在一个单步格式的基础上构造了一个新的隐式系数矩阵分裂法来数值求解可压Navier-St-okes方程。对方程中的无粘项部分利用守恒型方程中流通量向量为一齐次函数这一特性,根据Jacobian矩阵特征值的符号而将流通向量分裂成两部分。在此基础上据风向而构造逼近于无粘项的差分格式。对方程中的粘性项部分利用算子附加修正的方法来改进计算的收敛过程。所建立的差分格式被用来数值求解Couette流以考查这一方法。 相似文献
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龙格库塔间断有限元方法在计算爆轰问题中的应用 总被引:1,自引:1,他引:0
构造求解带源项守恒律方程组的龙格库塔间断有限元(RKDG)方法,并分别结合源项的Strang分裂法和无分裂法数值求解模型守恒律方程和反应欧拉方程.为了和有限体积型WENO方法进行比较,设计计算源项的WENO重构格式.对一维带源项守恒律的计算表明,对于非刚性问题,RKDG方法比有限体积型WENO方法的误差更小;对于刚性问题,RKDG方法对于间断面位置的捕捉更为精确.对于一二维爆轰波问题的计算结果表明,RKDG方法对爆轰波结构的分辨和爆轰波位置的捕捉能力更强. 相似文献
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二维交错网格的GAUSS型格式 总被引:2,自引:0,他引:2
利用Gauss型求积公式在交错网格的情况下构造了一类不需解Riemann问题的求解二维双曲守恒律的二阶显式Gauss型差分格式,该格式在CFL条件限制下为MmB格式.并将格式推广到二维方程组,进行了数值试验. 相似文献
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讨论一维和二维非线性Schr(o)dinger (NLS)方程的数值求解.基于扩散广义黎曼问题的数值流量,构造一种直接间断Galerkin方法(DDG)求解非线性Schr(o)dinger方程.证明该方法L2稳定性,并说明DDG格式是一种守恒的数值格式.对一维NLS方程的计算表明,DDG格式能够模拟各种孤立子形态,而且可以保持长时间的高精度.二维NLS方程的数值结果显示该方法的高精度和捕捉大梯度的能力. 相似文献
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Selection of near infrared spectral information based on section combination moving window partial least squares北大核心CSCD 下载免费PDF全文
Chen Y.Gao Z.Yu X.Zhu D.Chen M.Yuan Q. 《应用光学》2017,(1):99-105
Selection of near infrared spectral information is research focus on the application of NIR, which enable to simplify the model and improve accuracy of prediction. Aiming at selecting optimal modeling spectral width of near infrared spectroscopy, section combination moving window partial least squares (SCMWPLS) is proposed in this paper. This method selects continuous modeling screened interval.by continuously varying size of moving window and cross validation. Taking Glucose solution near-infrared spectroscopy as test specimen, near infrared prediction models are established respectively by proposed method, and traditional interval partial least squares (IPLS) and moving window partial least squares (MWPLS). Comparing proposed method with two traditional methods, squares prediction RMSE is decreased by 44% and 25% respectively. © 2017, Editorial Board, Journal of Applied Optics. All right reserved. 相似文献
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两种偏最小二乘分光光度法同时测定三组分混合物 总被引:1,自引:0,他引:1
本文研究两种偏最小二乘法(经典编最小二乘法(CPLS)和基于核心矩阵的偏最小二乘法(KPLS)同时测定三组分混合物,根据数学原理编制三个程序(SPGRAFA,SPGRPLS和SPGRKPLS)执行这些计算,八个误差函数用以推断因子数目,因为核心矩阵维数小于原始数据矩阵,所以KPLS法适于计算具有较多光谱数和较少样品数的数据矩阵,实验结果显示对相互重叠的光谱用这两种方法均能获得令人满意且十分吻合的结 相似文献
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波长选择是光谱建模分析的重要步骤。研究了近红外光谱法分析油页岩含油率过程中的波长选择方法,用以剔除光谱数据中的冗余信息和干扰信息,提高分析模型的建模效率和预测能力。分别采用相关系数法(CC)、移动窗口偏最小二乘法(MWPLS)和无信息变量消除法(UVE)对油页岩近红外漫反射光谱数据的波长区间进行了选择,研究了不同阈值、窗口宽度和噪声矩阵对上述方法的影响,建立了所选择波长处的反射率数据和样品含油率标准值间的偏最小二乘(PLS)分析模型,比较了上述方法的选择效果。结果表明:与使用全谱数据建模相比,采用上述方法筛选过的光谱数据均能提高模型的建模效率和预测能力,其中经UVE法筛选后的光谱数据仅占全谱数据总数的22.8%,模型的RMSECV却降低了9.3%,RMSEP降低了4.5%。 相似文献
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《Physics letters. A》2019,383(19):2235-2240
The total least squares (TLS) method is widely used in data-fitting. Compared with the least squares fitting method, the TLS fitting takes into account not only observation errors, but also errors from the measurement matrix of the variables. In this work, the TLS problem is transformed to finding the ground state of a Hamiltonian matrix. We propose quantum algorithms for solving this problem based on quantum simulation of resonant transitions. Our algorithms can achieve at least polynomial speedup over the known classical algorithms. 相似文献
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Meshless analysis of an improved element-free Galerkin method for linear and nonlinear elliptic problems 下载免费PDF全文
We first give a stabilized improved moving least squares(IMLS) approximation, which has better computational stability and precision than the IMLS approximation. Then, analysis of the improved element-free Galerkin method is provided theoretically for both linear and nonlinear elliptic boundary value problems. Finally, numerical examples are given to verify the theoretical analysis. 相似文献
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A unifying theoretical and algorithmic framework for least squares methods of estimation in diffusion tensor imaging 总被引:4,自引:0,他引:4
Koay CG Chang LC Carew JD Pierpaoli C Basser PJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,182(1):115-125
A unifying theoretical and algorithmic framework for diffusion tensor estimation is presented. Theoretical connections among the least squares (LS) methods, (linear least squares (LLS), weighted linear least squares (WLLS), nonlinear least squares (NLS) and their constrained counterparts), are established through their respective objective functions, and higher order derivatives of these objective functions, i.e., Hessian matrices. These theoretical connections provide new insights in designing efficient algorithms for NLS and constrained NLS (CNLS) estimation. Here, we propose novel algorithms of full Newton-type for the NLS and CNLS estimations, which are evaluated with Monte Carlo simulations and compared with the commonly used Levenberg-Marquardt method. The proposed methods have a lower percent of relative error in estimating the trace and lower reduced chi2 value than those of the Levenberg-Marquardt method. These results also demonstrate that the accuracy of an estimate, particularly in a nonlinear estimation problem, is greatly affected by the Hessian matrix. In other words, the accuracy of a nonlinear estimation is algorithm-dependent. Further, this study shows that the noise variance in diffusion weighted signals is orientation dependent when signal-to-noise ratio (SNR) is low (相似文献
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Methods of nonnegative tensor factorization (NTF), such as NTF1, NTF2, etc., are extension of nonnegative matrix factorization (NMF) for multi-way data analysis. As an existing NTF method, nonnegative Tucker3 decomposition (NTD) is researched for three-way decomposition in this paper. Firstly, an approach utilizing matrix exponentials built on Tikhonov-type regularization to enforce sparseness is proposed to extract image features instead of exclusively using Tucker tensor decomposition. Meanwhile, updating algorithms, derived from updating rules of NMF, are allowed to efficiently implement updating of mode matrices and core tensors alternatively for accuracy. Then, experimental cases of alternating least squares (ALS) and conjugate nonnegative constraints, called nonnegative alternating least squares (NALS), are studied to remedy data overfitting in computing procedures. Lastly, the proposed method exhibits more advantageous results than other algorithms of Tucker3 for feature extraction, thanks to computer simulations performed in the context of data analysis. 相似文献
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Luman Jia Yi Gu Qingxian Zhang Jian Zhang Xiaolan Yan Yifan Zhang Youjing Wang Liangquan Ge 《X射线光谱测定》2023,52(1):22-27
In energy dispersive X-ray fluorescence analysis (EDXRF), many baseline estimation algorithms have been proposed for the accurate characteristic peak area. However, the true value of the characteristic peak area of measured spectrum is unknown and cannot be used to evaluate the accuracy of the baseline estimation algorithms. In this article, an assessment method was proposed based on Monte Carlo simulation, which can obtain the characteristic peak area, and evaluate the accuracy of the baseline estimation algorithms directly. Meanwhile, the accuracy and practicality of four baseline estimation algorithms were evaluated by the assessment method, which include statistics-sensitive nonlinear iterative peak-clipping (SINP), fast Fourier transform (FFT), adaptive iteratively reweighted penalized least squares (AirPLS), and automated iterative moving averaging (AIMA). Comparing the relative error of the characteristic peak area, AirPLS gave the best performance for baseline estimation in EDXRF. 相似文献