ma5251: spectral methods & applications weizhu bao department of mathematics & center for...
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MA5251: Spectral Methods & Applications
Weizhu Bao
Department of Mathematics & Center for Computational Science and Engineering
National University of SingaporeEmail: [email protected]
URL: http://www.math.nus.edu.sg/~bao
Contents
Introduction and Preliminaries– Some numerical examples – Review of different numerical methods of PDE– Historical background of spectral methods– Some examples of spectral methods– Fourier series and orthogonal polynomials – Review of iterative solvers and preconditioning– Review of time discretization methods
Spectral-Collocation Methods– Introduction– Differentiation matrices– Fourier, Chebyshev collocation methods
Contents
Spectral-Galerkin methods– Introduction– Fourier spectral method– Legendre spectral method– Chebyshev spectral method– Error estimates
Spectral methods in unbounded domains – Introduction– Hermite spectral method– Laguerre specreal methods,….
Contents
Applications– In fluid dynamics– In heat transfer– In material sciences– In quantum physics and nonlinear optics– In plasma and particle physics– In biology– …………..
Main numerical methods for PDEs
Finite difference method (FDM) – MA5233– Advantages:
• Simple and easy to design the scheme• Flexible to deal with the nonlinear problem• Widely used for elliptic, parabolic and hyperbolic equations• Most popular method for simple geometry, ….
– Disadvantages:• Not easy to deal with complex geometry • Not easy for complicated boundary conditions• ……..
Main numerical methods
Finite element method (FEM) – MA5240– Advantages:
• Flexible to deal with problems with complex geometry and complicated boundary conditions
• Keep physical laws in the discretized level• Rigorous mathematical theory for error analysis• Widely used in mechanical structure analysis, computational fluid
dynamics (CFD), heat transfer, electromagnetics, …– Disadvantages:
• Need more mathematical knowledge to formulate a good and equivalent variational form
Main numerical methods
Spectral method – This module– High (spectral) order of accuracy– Usually restricted for problems with regular geometry– Widely used for linear elliptic and parabolic equations on
regular geometry– Widely used in quantum physics, quantum chemistry, material
sciences, …– Not easy to deal with nonlinear problem– Not easy to deal with hyperbolic problem– …..
Main numerical methods
Finite volume method (FVM) – MA5250– Flexible to deal with problems with complex geometry and complicated
boundary conditions– Keep physical laws in the discretized level– Widely used in CFD
Boundary element method (BEM)– Reduce a problem in one less dimension– Restricted to linear elliptic and parabolic equations– Need more mathematical knowledge to find a good and equivalent
integral form– Very efficient fast Poisson solver when combined with the fast multipole
method (FMM), …..
Historical background
Method of weighted residuals (MWR) – Finlayson & Scriven (1966)
– Trial functions (or expansion or approximation functions): are used as the basis functions for a truncated series expansion of the solution.
– Test functions (or weight functions): are used to ensure that the differential equation is satisfied as closely as possible by the truncated series expansion.
– This is achieved by minimizing the residual, i.e. the error in the differential equation produced by using the truncated expansion instead of the exact solution, with respect to a suitable norm.
– An equivalent requirement is that the residual satisfy a suitable orthogonality condition with respect to each of the test functions.
Historical background
Trial functions– Spectral method: infinitely differentiable global functions, i.e.
eigenfunctions of singular Sturm-Liouville problems– Finite Element Method (FEM): partition the domain into small elements,
and a trial function (usually polynomial) is specified in each element and thus local in character & well suited for handling complex geometries.
– Finite Difference Method (FDM): similar as FEM.
Test functions– Spectral methods: three different ways– FEM: similar as trial functions– FDM: Dirac delta functions centered at the grid points
Historical background
Different test functions of spectral methods– Galerkin method: same as the trial functions which are infinitely
smooth functions & individually satisfy the boundary conditions. The differential equation is enforced by requiring that the integral of the residual times each test function be zero.
– Collocation method: Dirac delta functions centered at the collocation points. The differential is required to be satisfied exactly at the collocation points.
– Spectral tau method: Similar as the Galerkin method except that no need the trial and test functions satisfy the boundary conditions. A supplementary set of equations is used to apply the boundary conditions.
Historical background
Collocation approach (simplest of the MWR) – Slater (1934); Kantorovic (1934); Frazer, Jones and Skan (1937).
Proper choice of trial functions and distribution of collocation points – Lanczos (1938)
Orthogonal collocation method – Clenshaw (1957); Clenshaw and Norton (1963); Wright (1964).
Earliest application of spectral methods to PDE – Kreiss and Oliger (1972)—Fourier method; Orszag (1972) –pseudospectral. Spectral-Galerkin method – Silberman (1954) in meteorological modeling; Orszag (1969, 1970); etc.
Historical background
– Theory of spectral method -- Gottlieb and Orszag (1977)
– Symposium Proceedings – Voigt, Gottlieb and Hussaini (1984)
– First International Conference on Spectral and High Order Methods (ICOSAHOM) -- Como, Italy in 1989. It becomes series conference every three years. The next one is
http://www.math.ntnu.no/icosahom/