A nonoverlapping domain decomposition method for orthogonal spline collocation problems

A nonoverlapping domain decomposition approach is used on uniform and matching grids to first define and then to compute the orthogonal spline collocation solution of the Dirichlet boundary value problem for Poisson's equation on an L-shaped region. We prove existence and uniqueness of the collocation solution and derive optimal order H-s-norm error bounds for s = 0, 1, 2. The collocation solution on two interfaces is computed using the preconditioned conjugate gradient method, and the collocation solution on three squares is computed by a matrix decomposition method that uses fast Fourier transforms. The total cost of the algorithm is O(N-2 log N), where the number of unknowns in the collocation solution is O(N-2).