# Hung-Tsai Huang

PhD
Professor Chairman
I-Shou University · Department of Applied Mathematics

## Publications

• ##### Article: Algorithm singularity of the null-field method for Dirichlet problems of Laplace׳s equation in annular and circular domains
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ABSTRACT: For circular domains with circular holes, the null field method (NFM) is proposed by Chen and his co-researchers when solving boundary integral equation (BIE). The explicit algebraic equations of the NFM are recently derived in Li et al. (2012) [33], and their conservative schemes are proposed in Lee et al. (2013) [28]. However, even for the Dirichlet problem of Laplace׳s equation, there may exist a singularity of the original boundary integral equation (BIE) and/or its numerical algorithms such as the NFM. Such a singularity is called the degenerate scale problem due to special domain scales, and was studied in Christiansen (1975) [22]. Since to bypass the singularity is imperative for both theory and computation, the degenerate scale problem has been extensively discussed in the literature. An algorithm singularity means the singularity of the coefficient matrix of collocation methods, but we confine ourselves to the singularity caused by the degenerate scale problem. So far, for the algorithm singularity of the NFM of degenerate scales, no advanced analysis exists, although a preliminary discussion was given in Chen and Shen (2007) and Lee et al. (2013) 15 and 28. In this paper, all kinds of field nodes of degenerate scales leading to algorithm singularity are revealed in detail. To remove singularity of discrete matrices and to restore good stability, several effective techniques are proposed. Numerical experiments are carried out to verify the theoretical analysis made. Based on the analysis and computation in this paper, not only can the algorithm singularity of the NFM be bypassed, but also the highly accurate solutions with good stability may be achieved.
Engineering Analysis with Boundary Elements 01/2014; 41:160–172. · 1.60 Impact Factor
• ##### Article: Conservative schemes and degenerate scale problems in the null-field method for Dirichlet problems of Laplace's equation in circular domains with circular holes
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ABSTRACT: Recently, the null-field method (NFM) has been proposed by Chen and his co-researchers for solving boundary value problems involving circular domains with circular holes. The explicit algebraic equations of the NFM are derived in our recent paper [31]. However, even for the Dirichlet problem of Laplace's equation, when the logarithmic capacity (transfinite diameter) CΓ=1CΓ=1 is given, the solutions may not exist, or not unique if existing, to cause a singularity of the discrete algebraic equations. The non-uniqueness of the solutions of Dirichlet problems by the boundary integral equations is first reported in Christiansen [20] due to some special geometry, and then in 14 and 15 called the degenerate scale problems. In this paper, the new conservative schemes of NFM are proposed. The conservative schemes can always bypass the degenerate scale problems; though numerically it causes a severe instability. A new pseudo-singularity property is discovered that only the minimal singular value σminσmin of the discrete matrices is infinitesimal to cause the instability. To restore good stability of the conservative schemes, the over-determined systems and the truncated singular value decomposition (TSVD) are proposed. The over-determined systems are more favorable than TSVD due to simpler algorithms and slightly better performances in error and stability. More importantly, such numerical techniques can also be used to deal with all the degenerate scale problems of the original NFM in 11, 12 and 13 as well as the boundary element method (BEM).
Engineering Analysis with Boundary Elements 01/2013; 37(1):95–106. · 1.60 Impact Factor
• ##### Article: The null-field method of Dirichlet problems of Laplace's equation on circular domains with circular holes
Zi-Cai Li, Hung-Tsai Huang, Cai-Pin Liaw, Ming-Gong Lee
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ABSTRACT: In this paper, the boundary errors are defined for the null-field method (NFM) to explore the convergence rates, and the condition numbers are derived for simple cases to explore numerical stability. The optimal convergence (or exponential) rates are discovered numerically. This paper is also devoted to seek better choice of locations for the field nodes of the fundamental solutions (FS) expansions. It is found that the location of field nodes Q does not affect much on convergence rates, but do have influence on stability. Let δδ denote the distance of Q to ∂S∂S. The larger δδ is chosen, the worse the instability of the NFM occurs. As a result, δ=0δ=0 (i.e., Q∈∂SQ∈∂S) is the best for stability. However, when δ>0δ>0, the errors are slightly smaller. Therefore, small δδ is a favorable choice for both high accuracy and good stability. This new discovery enhances the proper application of the NFM.
Engineering Analysis with Boundary Elements 03/2012; 36(3):477–491. · 1.60 Impact Factor
• ##### Article: Effective condition number for weighted linear least squares problems and applications to the Trefftz method
Yi-min Wei, Tzon-Tzer Lu, Hung-Tsai Huang, Zi-Cai Li
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ABSTRACT: In [27], the effective condition number Cond_eff is developed for the linear least squares problem. In this paper, we extend the effective condition number for weighted linear least squares problem with both full rank and rank-deficient cases. We apply the effective condition number to the collocation Trefftz method (CTM) [29] for Laplace's equation with a crack singularity, to prove that Cond_eff =O(L) and Cond =O(L1/2(2)L), where L is the number of singular particular solutions used. The Cond grows exponentially as L increases, but Cond_eff is only O(L). The small effective condition number explains well the high accuracy of the TM solution, but the huge Cond cannot.
Engineering Analysis with Boundary Elements 01/2012; 36(1):53–62. · 1.60 Impact Factor
• ##### Article: Effective Condition Number of Finite Difference Method for Poisson's Equation Involving Boundary Singularities
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ABSTRACT: For solving the linear algebraic equations Ax = b with the symmetric and positive definite matrix A, the effective condition number Cond_eff is defined in [66. Z.C. Li , C.S. Chien , and H.T. Huang ( 2007 ). Effective condition number for finite difference method . J. Comp. Appl. Math. 198 : 208 – 235 . [CrossRef], [Web of Science ®]View all references, 1010. Z.C. Li and H.T. Huang ( 2008 ). Effective condition number for numerical partial differential equations . Numer. Linear Algebra Applications 15 : 575 – 594 . [CrossRef], [Web of Science ®]View all references] by following Chan and Foulser [22. T.F. Chan and D.E. Foulser ( 1988 ). Effectively well-conditioned linear systems . SIAM J. Sci. Stat. Comput. 9 : 963 – 969 . [CrossRef], [Web of Science ®]View all references] and Rice [1414. J.R. Rice ( 1981 ). Matrix Computations and Mathematical Software . McGraw-Hill , New York . View all references]. The Cond_eff is smaller, or much smaller, than the traditional condition number Cond. Besides, the simplest condition number Cond_EE is also defined in [66. Z.C. Li , C.S. Chien , and H.T. Huang ( 2007 ). Effective condition number for finite difference method . J. Comp. Appl. Math. 198 : 208 – 235 . [CrossRef], [Web of Science ®]View all references, 1010. Z.C. Li and H.T. Huang ( 2008 ). Effective condition number for numerical partial differential equations . Numer. Linear Algebra Applications 15 : 575 – 594 . [CrossRef], [Web of Science ®]View all references]. This article studies a popular model of Poisson's equation involving the boundary singularities by the finite difference method using the local refinements of grids. The bounds of Cond_EE are derived to display theoretically that the effective condition number is significantly smaller than the Cond. In this article, by exploring local refinement properties, we derive the bounds of effective condition numbers up to O(1) and at least o(h −1/2) for the maximal step size h. They are significant improvements compared with the bound O(h −3/2), which is established in [66. Z.C. Li , C.S. Chien , and H.T. Huang ( 2007 ). Effective condition number for finite difference method . J. Comp. Appl. Math. 198 : 208 – 235 . [CrossRef], [Web of Science ®]View all references, 1010. Z.C. Li and H.T. Huang ( 2008 ). Effective condition number for numerical partial differential equations . Numer. Linear Algebra Applications 15 : 575 – 594 . [CrossRef], [Web of Science ®]View all references]. Therefore, the study of effective condition number in this article reaches a new comprehensive and advanced level.
Numerical Functional Analysis and Optimization 06/2011; 32(6):659-681. · 0.50 Impact Factor
• ##### Article: Stability analysis via condition number and effective condition number for the first kind boundary integral equations by advanced quadrature methods, a comparison
Jin Huang, Hung-Tsai Huang, Zi-Cai Li, Yimin Wei
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ABSTRACT: In our previous study [Huang et al., 2008, 2009, 2010 [21], [24] and [20]; Huang and Lu, 2004 [22] and [23]; Lu and Huang, 2000 [38]], we have proposed advanced (i.e., mechanical) quadrature methods (AQMs) for solving the boundary integral equations (BIEs) of the first kind. These methods have high accuracy O(h3), where h=max1⩽m⩽dhm and hm (m=1,…,d) are the mesh widths of the curved edge Γm. The algorithms are simple and easy to carry out, because the entries of discrete matrix are explicit without any singular integrals. Although the algorithms and error analysis of AQMs are discussed in Huang et al. (2008, 2009, 2010) [21], [24] and [20], Huang and Lu (2004) [22] and [23], Lu and Huang (2000) [38], there is a lack of systematic stability analysis. The first aim of this paper is to explore a new and systematic stability analysis of AQMs based on the condition number (Cond) and the effective condition number (Cond_eff) for the discrete matrix Kh. The challenging and difficult lower bound of the minimal eigenvalue is derived in detail for the discrete matrix of AQMs for a typical BIE of the first kind. We obtain Cond=O(hmin−1) and Cond_eff=O(hmin−1), where hmin=min1⩽m⩽dhm, to display excellent stability. Note that Cond_eff = O(Cond) is greatly distinct to the case of numerical partial differential equations (PDEs) in Li et al. (2007, 2008, 2009, 2010) [26], [31], [32], [33], [34], [35], [36] and [37], Li and Huang (2008) [27], [28], [29] and [30], Huang and Li (2006) [19] where Cond_eff is much smaller than Cond. The second aim of this paper is to explore intrinsic characteristics of Cond_eff, and to make a comparison with numerical PDEs. Numerical experiments are carried out for three models with smooth and singularity solutions, to support the analysis made.
Engineering Analysis with Boundary Elements 04/2011; 35(4):667-677. · 1.60 Impact Factor
• ##### Article: Ill‐conditioning of the truncated singular value decomposition, Tikhonov regularization and their applications to numerical partial differential equations
Zi-Cai Li, Hung-Tsai Huang, Yimin Wei
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ABSTRACT: This paper explores some intrinsic characteristics of accuracy and stability for the truncated singular value decomposition (TSVD) and the Tikhonov regularization (TR), which can be applied to numerical solutions of partial differential equations (numerical PDE). The ill-conditioning is a severe issue for numerical methods, in particular when the minimal singular value sigmamin of the stiffness matrix is close to zero, and when the singular vector umin of σmin is highly oscillating. TSVD and TR can be used as numerical techniques for seeking stable solutions of linear algebraic equations. In this paper, new bounds are derived for the condition number and the effective condition number which can be used to improve ill-conditioning by TSVD and TR. A brief error analysis of TSVD and TR is also made, since both errors and condition number are essential for the numerical solution of PDE. Numerical experiments are reported for the discrete Laplace operator by the method of fundamental solutions. Copyright © 2011 John Wiley & Sons, Ltd.
Numerical Linear Algebra with Applications 02/2011; 18(2):205 - 221. · 1.20 Impact Factor
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##### Article: Effective condition number and its applications
Zi-Cai Li, Hung-Tsai Huang, Jeng-Tzong Chen, Yimin Wei, Z.-C Li, H.-T Huang, J.-T Chen
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ABSTRACT: Consider the over-determined system Fx = b where F ∈ R m×n , m ≥ n and rank (F) = r ≤ n, the effective condition number is defined by Cond_eff = b σ r x , where the singular values of F are given as σ max = σ 1 ≥ σ 2 ≥ · · · ≥ σ r > 0 and σ r +1 = · · · = σ n = 0. For the general perturbed system (A+A)(x +x) = b+b Communicated by N. Yan. Partial results of this paper were represented at the Mini symposium on Collocation and Trefftz Method for the 7th 123 88 Z.-C. Li et al. involving both A and b, the new error bounds pertinent to Cond_eff are derived. Next, we apply the effective condition number to the solutions of Motz's problem by the collocation Trefftz methods (CTM). Motz's problem is the benchmark of singu-larity problems. We choose the general particular solutions v L = L k=0 d k (r R p) k+ 1 2 cos(k + 1 2)θ with a radius parameter R p . The CTM is used to seek the coefficients d i by satisfying the boundary conditions only. Based on the new effective condition num-ber, the optimal parameter R p = 1 is found. which is completely in accordance with the numerical results. However, if based on the traditional condition number Cond, the optimal choice of R p is misleading. Under the optimal choice R p = 1, the Cond grows exponentially as L increases, but Cond_eff is only linear. The smaller effective condition number explains well the very accurate solutions obtained. The error anal-ysis in [14,15] and the stability analysis in this paper grant the CTM to become the most efficient and competent boundary method.
Computing 08/2010; 89:87-112. · 0.81 Impact Factor
• ##### Article: Comparisons of fundamental solutions and particular solutions for Trefftz methods
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ABSTRACT: In the Trefftz method (TM), the admissible functions satisfying the governing equation are chosen, then only the boundary conditions are dealt with. Both fundamental solutions (FS) and particular solutions (PS) satisfy the equation. The TM using FS leads to the method of fundamental solutions (MFS), and the TM using PS to the method of particular solutions (MPS). Since the MFS is one of TM, we may follow our recent book [20,21] to provide the algorithms and analysis. Since the MFS and the MPS are meshless, they have attracted a great attention of researchers. In this paper numerical experiments are provided to support the error analysis of MFS in Li [15] for Laplace's equation in annular shaped domains. More importantly, comparisons are made in analysis and computation for MFS and MPS. From accuracy and stability, the MPS is superior to the MFS, the same conclusion as given in Schaback [24]. The uniform FS is simpler and the algorithms of MFS are easier to carry out, so that the computational efforts using MFS are much saved. Since today, the manpower saving is the most important criterion for choosing numerical methods, the MFS is also beneficial to engineering applications. Hence, both MFS and MPS may serve as modern numerical methods for PDE.
Engineering Analysis With Boundary Elements - ENG ANAL BOUND ELEM. 01/2010; 34(3):248-258.
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##### Article: Superconvergence of high order FEMs for eigenvalue problems with periodic boundary conditions
H.-T Huang, S.-L Chang, C.-S Chien, Z.-C Li
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ABSTRACT: a b s t r a c t We study Adini's elements for nonlinear Schrödinger equations (NLS) defined in a square box with peri-odic boundary conditions. First we transform the time-dependent NLS to a time-independent stationary state equation, which is a nonlinear eigenvalue problem (NEP). A predictor–corrector continuation method is exploited to trace solution curves of the NEP. We are concerned with energy levels and super-fluid densities of the NLS. We analyze superconvergence of the Adini elements for the linear Schrödinger equation defined in the unit square. The optimal convergence rate Oðh 6 Þ is obtained for quasiuniform ele-ments. For uniform rectangular elements, the superconvergence Oðh 6þp Þ is obtained for the minimal eigenvalue, where p ¼ 1 or p ¼ 2. The theoretical analysis is confirmed by the numerical experiments. Other kinds of high order finite element methods (FEMs) and the superconvergence property are also investigated for the linear Schrödinger equation. Finally, the Adini elements-continuation method is exploited to compute energy levels and superfluid densities of a 2D Bose–Einstein condensates (BEC) in a periodic potential. Numerical results on the ground state as well as the first few excited-state solutions are reported.
Computer Methods in Applied Mechanics and Engineering 04/2009; 198(30). · 2.62 Impact Factor
• ##### Article: Effective condition number for the finite element method using local mesh refinements
Zi-Cai Li, Hung-Tsai Huang
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ABSTRACT: This is a continued study but at advanced levels of effective condition number in [Z.C. Li, C.S. Chien, H.T. Huang, Effective condition number for finite difference method, J. Comput. Appl. Math. 198 (2007) 208–235; Z.C. Li, H.T. Huang, Effective condition number for numerical partial differential equations, Numer. Linear Algebra Appl. 15 (2008) 575–594] for stability analysis. To approximate Poisson's equation with singularity by the finite element method (FEM), the adaptive mesh refinements are an important and popular technique, by which, the FEM solutions with optimal convergence rates can be obtained. The local mesh refinements are essential to FEM for solving complicated problems with singularities, and they have been used for three decades. However, the traditional condition number is given by in Strang and Fix [G. Strang, G.J. Fix, An Analysis of the Finite Element Method, Prentice-Hall, Englewood Cliffs, NJ, 1973], where hmin is the minimal length of elements. Since hmin is infinitesimal near the singular points, Cond is huge. Such a dilemma can be bypassed by small effective condition number. In this paper, the bounds of the simplified effective condition number Cond_EE are derived as O(1), O(h−1.5) or O(h−0.5), where is the maximal length of elements. Evidently, Cond_EE is much smaller than Cond. The numerical experiments are carried out, to verify the stability analysis. Small effective condition numbers explain well the satisfactory FEM solutions obtained. This paper provides a stability justification for the adaptive mesh refinements used in FEM. Compared with [Z.C. Li, C.S. Chien, H.T. Huang, Effective condition number for finite difference method, J. Comput. Appl. Math. 198 (2007) 208–235; Z.C. Li, H.T. Huang, Effective condition number for numerical partial differential equations, Numer. Linear Algebra Appl. 15 (2008) 575–594], the analysis in this paper is more difficult and challenging, its proof techniques are new and intriguing, and the results are more important and useful.
Applied Numerical Mathematics. 01/2009; 59(8):1779-1795.
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##### Article: Error Analysis of Trefftz Methods for Laplace's Equations and Its Applications
Z C Li, T T Lu, H T Huang, D Cheng
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ABSTRACT: For Laplace's equation and other homogeneous elliptic equations, when the particular and fundamental solutions can be found, we may choose their linear combination as the admissible functions, and obtain the expansion coeffi-cients by satisfying the boundary conditions only. This is known as the Trefftz method (TM) (or boundary approximation methods). Since the TM is a meshless method, it has drawn great attention of researchers in recent years, and Inter. Work-shops of TM and MFS (i.e., the method of fundamental solutions). A number of efficient algorithms, such the collocation algorithms, Lagrange multiplier methods, etc., have been developed in computation. However, there still exists a gap of con-vergence and errors between computation and theory. In this paper, convergence analysis and error estimates are explored for Laplace's equations with the solution u ∈ H k (k > 1 2), to achieve polynomial convergence rates. Such a basic theory is im-portant for TM and MFS and their further developments. Numerical experiments are provided to support the analysis and to display the significance of its applica-tions.
Tech Science Press CMES Copyright. 01/2009; 5252:39-8139.
• ##### Article: Superconvergence of bi-k-Lagrange elements for eigenvalue problems.
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ABSTRACT: We study superconvergence of bi-k-Lagrange elements for parameter-dependent problems where k⩾2. We show that the superconvergence rate of the bi-k-Lagrange elements is two orders higher than that of the kth-order Lagrange elements. This is a significant improvement of the previous results [C.-S. Chien, H.T. Huang, B.-W. Jeng, Z.C. Li, Superconvergence of FEMs and numerical continuation for parameter-dependent problems with folds, Int. J. Bifurcation Chaos 18 (2008) 1321–1336], which is only one order (or a half order) higher than that of the latter. Next, we apply the bi-k-Lagrange elements to the computations of energy levels and wave functions of two-dimensional (2D) Bose–Einstein condensates (BEC), and BEC in a periodic potential. Sample numerical results are reported.
Computer Physics Communications 01/2009; 180:2268-2282. · 3.08 Impact Factor
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##### Article: New expansions of numerical eigenvalues by Wilson’s element
Qun Lin, Hung-Tsai Huang, Zi-Cai Li
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ABSTRACT: The paper explores new expansions of eigenvalues for −Δu=λρu in S with Dirichlet boundary conditions by Wilson’s element. The expansions indicate that Wilson’s element provides lower bounds of the eigenvalues. By the extrapolation or the splitting extrapolation, the O(h4) convergence rate can be obtained, where h is the maximal boundary length of uniform rectangles. Numerical experiments are carried to verify the theoretical analysis made. It is worth pointing out that these results are new, compared with the recent book, Lin and Lin [Q. Lin, J. Lin, Finite Element Methods; Accuracy and Improvement, Science Press, Beijing, 2006].
Journal of Computational and Applied Mathematics 01/2009; · 0.99 Impact Factor
• ##### Article: Stability analysis of Trefftz methods for the stick-slip problem
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ABSTRACT: The stick-slip problem is a two-dimensional Stokes flow problem, and is classified into biharmonic equation with crack singularities. The collocation Trefftz method (CTM) is used to provide the very accurate solutions and leading coefficients. In this paper, the error analysis is made, to show the exponential convergence rates, and the new stability analysis is explored more in detail. We derive the bounds of effective and traditional condition numbers, to have the polynomial and the exponential growth rates, respectively. The moderate effective condition number is a suitable criterion of stability for the CTM solution of the stick-slip problem, while the huge condition number is misleading. Besides, numerical experiments are carried out to support the stability analysis. Hence the effective condition number becomes a new trend of stability for numerical partial differential equations.
Engineering Analysis with Boundary Elements. 01/2009;
• ##### Article: On solution uniqueness of elliptic boundary value problems.
Zi-Cai Li, Qing Fang, Hung-Tsai Huang, Yimin Wei
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ABSTRACT: In this paper, we consider the problem of solution uniqueness for the second order elliptic boundary value problem, by looking at its finite element or finite difference approximations. We derive several equivalent conditions, which are simpler and easier than the boundedness of the entries of the inverse matrix given in Yamamoto et al., [T. Yamamoto, S. Oishi, Q. Fang, Discretization principles for linear two-point boundary value problems, II, Numer. Funct. Anal. Optim. 29 (2008) 213–224]. The numerical experiments are provided to support the analysis made. Strictly speaking, the uniqueness of solution is equivalent to the existence of nonzero eigenvalues in the corresponding eigenvalue problem, and this condition should be checked by solving the corresponding eigenvalue problems. An application of the equivalent conditions is that we may discover the uniqueness simultaneously, while seeking the approximate solutions of elliptic boundary equations.
Journal of Computational and Applied Mathematics 01/2009; 233:293-307. · 0.99 Impact Factor
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##### Article: Superconvergence and stability for boundary penalty techniques of finite difference methods
Zi-Cai Li, Hung-Tsai Huang, Jin Huang
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ABSTRACT: The finite difference method (FDM) is used for Dirichlet problems of Poisson's equation, and the Dirichlet boundary condition is dealt with by boundary penalty techniques. Two penalty techniques, penalty-integrals and penalty-collocations (i.e., fixing), are proposed in this paper. The error bounds in the discrete H1 norm and the infinite norms are derived. The stability analysis is based on the new effective condition number (Cond_eff) but not on the traditional condition number (Cond). The bounds of Cond_eff are explored to display that both the penalty-integral and the penalty-collocation techniques have good stability; the huge Cond is misleading. Since the penalty-collocation technique (i.e., the fixing technique) is simpler, it has been applied in engineering problem for a long time. It is worthy to point out that this paper is the first time to provide a theoretical justification for such a popular penalty-collocation (fixing) technique. Hence the penalty-collocation is recommended for dealing with the complicated constraint conditions such as the clamped and the simply support boundary conditions of biharmonic equations. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2008
Numerical Methods for Partial Differential Equations 04/2008; 24(3):972 - 990. · 1.21 Impact Factor
• ##### Article: Effective condition number for numerical partial differential equations
Zi-Cai Li, Hung-Tsai Huang
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ABSTRACT: In this paper, the new computational formulas are derived for the effective condition number Cond_eff, and the new error bounds involved in both Cond and Cond_eff are developed. A theoretical analysis is provided to support some conclusions in Banoczi et al. (SIAM J. Sci. Comput. 1998; 20:203–227). For the linear algebraic equations solved by the Gaussian elimination or the QR factorization (QR), the direction of the right-hand vector is insignificant for the solution errors, but such a conclusion is invalid for the finite difference method for Poisson's equation. The effective condition number is important to the numerical partial differential equations, because the discretization errors are dominant. Copyright © 2008 John Wiley & Sons, Ltd.
Numerical Linear Algebra with Applications 02/2008; 15(7):575 - 594. · 1.20 Impact Factor
• ##### Article: Effective condition number for simplified hybrid Trefftz methods
Zi-Cai Li, Hung-Tsai Huang
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ABSTRACT: The simplified hybrid Trefftz method was first proposed in Trefftz [Ein Gegenstuck zum Ritz'schen Verfahren. In: Proceedings of the second international congress on applied mechanics, Zurich, 1926. p. 131–7] in 1926 for solving Laplace's equation, where the harmonic functions are chosen as admissible functions, and their linear combination is sought to satisfy the boundary conditions. The error analysis of the hybrid TM is provided in [Li ZC, Chen YL, Georgiou GG, Xenohontos C. Special boundary approximation methods for Laplace equation problems with boundary singularities—applications to the Motz problem. Int Comput Math Appl 2006;51:115–42; Li ZC, Lu TT, Hu HY, Cheng AH-D. Trefftz and collocation methods. Southampton: WIT Publishers; 2007], but no stability analysis exists so far. Also the simplified hybrid techniques have been applied for the TM to couple with the finite element method (FEM) in our previous study and only the error analysis has been made. Hence, the stability analysis is important for the simplified hybrid TM. In this paper, we will apply the effective condition number Cond_eff. For the original hybrid TM [Ein Gegenstuck zum Ritz'schen Verfahren. In: Proceedings of the second international congress on applied mechanics, Zurich, 1926. p. 131–7], uniform particular solutions satisfying the governed equation (e.g., the harmonic functions satisfying Laplace's equation) were chosen. In general, piecewise particular solutions can be used for wide application of the hybrid TM, and the interior continuity conditions may be dealt with by hybrid techniques. Their algorithms and error analysis are provided in [Huang HT, Li ZC, Herrera I. Coupling techniques of Trefftz methods. Technical Report, Department of Applied Mathematics, National Sun Yat-Sen University, Kaohsiung, Taiwan; 2006] without stability analysis. In this paper, two cases of the simplified hybrid TM are considered: Case I: uniform particular solutions used, and Case II: piecewise particular solutions used. It is proved that both Cond_eff and Cond grow exponentially, with respect to the number of particular solutions used. In Case I, Cond is huge and Cond_eff is significantly smaller than Cond; but in Case II, Cond is moderately large, and Cond_eff is significantly smaller than Cond. Hence the ill-conditioning of the simplified hybrid TM for Case II is not severe. Such theoretical results have been validated by the numerical experiments. The study of Cond_eff in this paper provides a complete and comprehensive knowledge of the simplified hybrid TM.
Engineering Analysis With Boundary Elements - ENG ANAL BOUND ELEM. 01/2008; 32(9):757-769.
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##### Article: Two-grid discretization schemes for nonlinear Schrödinger equations
C.-S Chien, H.-T Huang, B.-W Jeng, Z.-C Li
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ABSTRACT: We study efficient two-grid discretization schemes with two-loop continuation algorithms for computing wave functions of two-coupled nonlinear Schrödinger equations defined on the unit square and the unit disk. Both linear and quadratic approximations of the operator equations are exploited to derive the schemes. The centered difference approximations, the six-node triangular elements and the Adini elements are used to discretize the PDEs defined on the unit square. The proposed schemes also can compute stationary solutions of parameter-dependent reaction–diffusion systems. Our numerical results show that it is unnecessary to perform quadratic approximations.
Journal of Computational and Applied Mathematics 01/2008; 214:549-571. · 0.99 Impact Factor