Accession Number : ADA329492

Title :   The PSEUDO-Inverse of the Derivative Operator in Polynomial Spectral Methods,

Corporate Author : INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA

Personal Author(s) : Loncaric, Josip

PDF Url : ADA329492

Report Date : JUL 1997

Pagination or Media Count : 17

Abstract : The matrix D - kI in polynomial approximations of order N is similar to a large Jordan block which is invertible for nonzero k but extremely sensitive to perturbation. Solving the problem (D - kI)f = g involves similarity transforms whose condition number grows as NI, which exceeds typical machine precision for N > 17. By using orthogonal projections, we reformulate the problem in terms of Q, the pseudo-inverse of D, and therefore its optimal preconditioner. The matrix Q in commonly used Chebyshev or Legendre representations is a simple tridiagonal matrix and its eigenvalues are small and imaginary. The particular solution of (I - kQ)f = Qg can be found for all real k at high resolutions and low computational cost (O(N) times faster than the commonly used Lanczos tau method). Boundary conditions are applied later by adding a multiple of the known homogeneous solution. In Chebyshev representation, machine precision results are achieved at modest resolution requirements. Multidimensional and higher order differential operators can also take advantage of the simple form of Q by factoring or preconditioning.

Descriptors :   *EIGENVALUES, *POLYNOMIALS, FOURIER TRANSFORMATION, MATRICES(MATHEMATICS), APPROXIMATION(MATHEMATICS), PERTURBATIONS, OPERATORS(MATHEMATICS), LAPLACE TRANSFORMATION.

Subject Categories : Numerical Mathematics

Distribution Statement : APPROVED FOR PUBLIC RELEASE