# Publication Citation

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Author(s): Sita Ramamurti; David E. Gilsinn; Bicubic B-Spline Surface Approximation of Invariant Tori October 20, 2010 The invariant torus of a coupled system of Van der Pol oscillators is approximated using bicubic B-splines. The paper considers the case of strong nonlinear coupling. In particular, the shapes of invariant torii for the Van der Pol coupling parameter $\lambda$ are computed in the range [0.1, 2.0]. Comparisons are given with results obtained by the MATLAB differential equation solver ode45. Very good normed residual errors of the determining equations for the approximate tori for the cases $\lambda = 0.1,\ 0.6$ are shown. At the upper limit of $\lambda = 2.0$ memory errors occured during the optimization phase for solving the determining equations so that full optimization for some knot sets was not achieved, but a visual comparison of the resulting invariant torus figure showed a close similarity to the solution using ode45. NIST Interagency/Internal Report (NISTIR) - 7731 32 pp. bicubic B-splines; determining equations; invariant torus; large parameter case; optimization; Van der Pol oscillators Software, Math Click here to retrieve PDF version of paper (2MB)