# American Institute of Mathematical Sciences

March  2021, 10(1): 129-153. doi: 10.3934/eect.2020054

## Uniform boundary observability with Legendre-Galerkin formulations of the 1-D wave equation

 1 INRIA, Villiers-lès-Nancy, F-54600, France 2 GIREF, Département de mathématiques et statistique, Université Laval, Québec, G1V 0A6, Canada

* Corresponding author: ludovick.gagnon@inria.fr

Received  January 2020 Revised  February 2020 Published  March 2021 Early access  May 2020

Fund Project: The research of José M. Urquiza is partially supported by the Natural Sciences and Engineering Research Council of Canada (NSERC)

We study the boundary observability of the 1-D homogeneous wave equation when using a Legendre-Galerkin semi-discretization method. It is already known that spurious high frequencies are responsible for its lack of uniformity with respect to the discretization parameter [4] which may prevent convergence in the approximation of the associated controllability problem. A classical remedy is to filter out the highest frequency components but this comes with a high computational cost in several space dimensions. We present here three remedies: a spectral filtering method, a mixed formulation (already used in the context of finite element method [14]) and a Nitsche's method. Our numerical results show that the uniform boundary observability inequalities are recovered. On the other hand, surprisingly, none of them seem to provide the trace (or direct) inequality uniformly, a property used to prove the convergence of the numerical controls [11]. However, our numerical tests suggest that convergence of the numerical controls is ensured when the uniform observability inequality holds.

Citation: Ludovick Gagnon, José M. Urquiza. Uniform boundary observability with Legendre-Galerkin formulations of the 1-D wave equation. Evolution Equations and Control Theory, 2021, 10 (1) : 129-153. doi: 10.3934/eect.2020054
##### References:
 [1] D. N. Arnold, An interior penalty finite element method with discontinuous elements, SIAM J. Numer. Anal., 19 (1982), 742-760.  doi: 10.1137/0719052. [2] L. Bales and I. Lasiecka, Negative norm estimates for fully discrete finite element approximations to the wave equation with nonhomogeneous ${L}_2$ Dirichlet boundary data, Math. Comp., 64 (1995), 89-115.  doi: 10.2307/2153324. [3] C. Bardos, G. Lebeau and J. Rauch, Sharp sufficient conditions for the observation, control, and stabilization of waves from the boundary, SIAM J. Control Optim., 30 (1992), 1024-1065.  doi: 10.1137/0330055. [4] T. Z. Boulmezaoud and J. M. Urquiza, On the eigenvalues of the spectral second order differentiation operator and application to the boundary observability of the wave equation, J. Sci. Comput., 31 (2007), 307-345.  doi: 10.1007/s10915-006-9106-8. [5] N. Burq and P. Gérard, Condition nécessaire et suffisante pour la contrôlabilité exacte des ondes, C. R. Math. Acad. Sci. Paris Sér. I Math., 325 (1997), 749-752.  doi: 10.1016/S0764-4442(97)80053-5. [6] C. Canuto, M. Y. Hussaini, A. Quarteroni and T. A. Zang, Spectral Methods, Scientific Computation, Springer-Verlag, Berlin, 2006. [7] C. Castro and S. Micu, Boundary controllability of a linear semi-discrete 1-D wave equation derived from a mixed finite element method, Numer. Math., 102 (2006), 413-462.  doi: 10.1007/s00211-005-0651-0. [8] C. Castro, S. Micu and A. Münch, Numerical approximation of the boundary control for the wave equation with mixed finite elements in a square, IMA J. Numer. Anal., 28 (2008), 186-214.  doi: 10.1093/imanum/drm012. [9] T. Chen and B. Francis, Optimal Sampled-data Control Systems, Communications and Control Engineering Series, Springer-Verlag London, Ltd., London, 1996. [10] S. Dolecki and D. L. Russell, A general theory of observation and control, SIAM J. Control Optim., 15 (1977), 185-220.  doi: 10.1137/0315015. [11] S. Ervedoza and E. Zuazua, The wave equation: Control and numerics, in Control of Partial Differential Equations, Lecture Notes in Mathematics, 2048, Springer, Berlin, Heidelberg, 2012,245–340. doi: 10.1007/978-3-642-27893-8_5. [12] S. Ervedoza and E. Zuazua, Numerical Approximation of Exact Controls for Waves, SpringerBriefs in Mathematics, Springer, New York, 2013. doi: 10.1007/978-1-4614-5808-1. [13] R. Glowinski, Ensuring well-posedness by analogy: Stokes problem and boundary control for the wave equation, J. Comput. Phys., 103 (1992), 189-221.  doi: 10.1016/0021-9991(92)90396-G. [14] R. Glowinski, W. Kinton and M. F. Wheeler, A mixed finite element formulation for the boundary controllability of the wave equation, Internat. J. Numer. Methods Engrg., 27 (1989), 623-635.  doi: 10.1002/nme.1620270313. [15] R. Glowinski, C. H. Li and J.-L. Lions, A numerical approach to the exact boundary controllability of the wave equation. I. Dirichlet controls: Description of the numerical methods, Japan J. Appl. Math., 7 (1990), 1-76.  doi: 10.1007/BF03167891. [16] M. J. Grote, A. Schneebeli and D. Schötzau, Discontinuous Galerkin finite element method for the wave equation, SIAM J. Numer. Anal., 44 (2006), 2408-2431.  doi: 10.1137/05063194X. [17] P. Hansbo, Nitsche's method for interface problems in computational mechanics, GAMM-Mitt., 28 (2005), 183-206.  doi: 10.1002/gamm.201490018. [18] J. S. Hesthaven and R. M. Kirby, Filtering in Legendre spectral methods, Math. Comp., 77 (2008), 1425-1452.  doi: 10.1090/S0025-5718-08-02110-8. [19] J. A. Infante and E. Zuazua, Boundary observability for the space semi-discretizations of the $1$-D wave equation, M2AN Math. Model. Numer. Anal., 33 (1999), 407-438.  doi: 10.1051/m2an:1999123. [20] V. Komornik, Exact Controllability and Stabilization. The Multiplier Method, RAM: Research in Applied Mathematics, Masson, Paris; John Wiley & Sons, Ltd., Chichester, 1994. [21] I. Lasiecka, J.-L. Lions and R. Triggiani, Nonhomogeneous boundary value problems for second order hyperbolic operators, J. Math. Pures Appl., 65 (1986), 149-192. [22] I. Lasiecka and R. Triggiani, Regularity of hyperbolic equations under $L_{2}(0, \, T;L_{2}(\Gamma))$-Dirichlet boundary terms, Appl. Math. Optim., 10 (1983), 275-286.  doi: 10.1007/BF01448390. [23] I. Lasiecka and R. Triggiani, Exact controllability of the Euler-Bernoulli equation with controls in the Dirichlet and Neumann boundary conditions: A nonconservative case, SIAM J. Control Optim., 27 (1989), 330-373.  doi: 10.1137/0327018. [24] I. Lasiecka and R. Triggiani, Exact controllability of the wave equation with Neumann boundary control, Appl. Math. Optim., 19 (1989), 243-290.  doi: 10.1007/BF01448201. [25] I. Lasiecka and R. Triggiani, Differential and algebraic riccati equations with applications to boundary/point control problems: Continuous theory and approximation theory, in Lecture Notes in Control and Information Sciences, 164, Springer-Verlag, Berlin, 1991. doi: 10.1007/BFb0006880. [26] J.-L. Lions, Contrôlabilité exacte, perturbations et stabilisation de systèmes distribués. Tome 1, in Research in Applied Mathematics, 8, Masson, Paris, 1988. [27] A. Marica and E. Zuazua, Symmetric Discontinuous Galerkin Methods for 1-D Waves. Fourier Analysis, Propagation, Observability and Applications, SpringerBriefs in Mathematics, Springer, New York, 2014. doi: 10.1007/978-1-4614-5811-1. [28] M. Negreanu and E. Zuazua, Convergence of a multigrid method for the controllability of a 1-d wave equation, C. R. Math. Acad. Sci. Paris, 338 (2004), 413-418.  doi: 10.1016/j.crma.2003.11.032. [29] J. Nitsche, Über ein Variationsprinzip zur Lösung von Dirichlet-Problemen bei Verwendung von Teilräumen, die keinen Randbedingungen unterworfen sind, Abh. Math. Sem. Univ. Hamburg, 36 (1971), 9-15.  doi: 10.1007/BF02995904. [30] J. Shen, Efficient spectral-Galerkin method. I. Direct solvers of second- and fourth-order equations using Legendre polynomials, SIAM J. Sci. Comput., 15 (1994), 1489-1505.  doi: 10.1137/0915089. [31] R. Triggiani, Exact boundary controllability on ${L}_2({\Omega})\times {H}^{-1}({\Omega})$ of the wave equation with Dirichlet boundary control acting on a portion of the boundary $\partial\Omega$, and related problems, Appl. Math. Optim., 18 (1988), 241-277.  doi: 10.1007/BF01443625. [32] M. Tucsnak and G. Weiss, Observation and Control for Operator Semigroups, Birkhäuser Advanced Texts: Basler Lehrbücher, Birkhäuser Verlag, Basel, 2009. doi: 10.1007/978-3-7643-8994-9. [33] H. Vandeven, On the eigenvalues of second-order spectral differentiation operators, Comput. Methods Appl. Mech. Engrg., 80 (1990), 313-318.  doi: 10.1016/0045-7825(90)90035-K. [34] T. Warburton and J. S. Hesthaven, On the constants in $hp$-finite element trace inverse inequalities, Comput. Methods Appl. Mech. Engrg., 192 (2003), 2765-2773.  doi: 10.1016/S0045-7825(03)00294-9. [35] E. Zuazua, Boundary observability for the finite-difference space semi-discretizations of the 2-D wave equation in the square, J. Math. Pures Appl., 78 (1999), 523-563.  doi: 10.1016/S0021-7824(98)00008-7. [36] E. Zuazua, Propagation, observation, and control of waves approximated by finite difference methods, SIAM Rev., 47 (2005), 197-243.  doi: 10.1137/S0036144503432862.

show all references

##### References:
 [1] D. N. Arnold, An interior penalty finite element method with discontinuous elements, SIAM J. Numer. Anal., 19 (1982), 742-760.  doi: 10.1137/0719052. [2] L. Bales and I. Lasiecka, Negative norm estimates for fully discrete finite element approximations to the wave equation with nonhomogeneous ${L}_2$ Dirichlet boundary data, Math. Comp., 64 (1995), 89-115.  doi: 10.2307/2153324. [3] C. Bardos, G. Lebeau and J. Rauch, Sharp sufficient conditions for the observation, control, and stabilization of waves from the boundary, SIAM J. Control Optim., 30 (1992), 1024-1065.  doi: 10.1137/0330055. [4] T. Z. Boulmezaoud and J. M. Urquiza, On the eigenvalues of the spectral second order differentiation operator and application to the boundary observability of the wave equation, J. Sci. Comput., 31 (2007), 307-345.  doi: 10.1007/s10915-006-9106-8. [5] N. Burq and P. Gérard, Condition nécessaire et suffisante pour la contrôlabilité exacte des ondes, C. R. Math. Acad. Sci. Paris Sér. I Math., 325 (1997), 749-752.  doi: 10.1016/S0764-4442(97)80053-5. [6] C. Canuto, M. Y. Hussaini, A. Quarteroni and T. A. Zang, Spectral Methods, Scientific Computation, Springer-Verlag, Berlin, 2006. [7] C. Castro and S. Micu, Boundary controllability of a linear semi-discrete 1-D wave equation derived from a mixed finite element method, Numer. Math., 102 (2006), 413-462.  doi: 10.1007/s00211-005-0651-0. [8] C. Castro, S. Micu and A. Münch, Numerical approximation of the boundary control for the wave equation with mixed finite elements in a square, IMA J. Numer. Anal., 28 (2008), 186-214.  doi: 10.1093/imanum/drm012. [9] T. Chen and B. Francis, Optimal Sampled-data Control Systems, Communications and Control Engineering Series, Springer-Verlag London, Ltd., London, 1996. [10] S. Dolecki and D. L. Russell, A general theory of observation and control, SIAM J. Control Optim., 15 (1977), 185-220.  doi: 10.1137/0315015. [11] S. Ervedoza and E. Zuazua, The wave equation: Control and numerics, in Control of Partial Differential Equations, Lecture Notes in Mathematics, 2048, Springer, Berlin, Heidelberg, 2012,245–340. doi: 10.1007/978-3-642-27893-8_5. [12] S. Ervedoza and E. Zuazua, Numerical Approximation of Exact Controls for Waves, SpringerBriefs in Mathematics, Springer, New York, 2013. doi: 10.1007/978-1-4614-5808-1. [13] R. Glowinski, Ensuring well-posedness by analogy: Stokes problem and boundary control for the wave equation, J. Comput. Phys., 103 (1992), 189-221.  doi: 10.1016/0021-9991(92)90396-G. [14] R. Glowinski, W. Kinton and M. F. Wheeler, A mixed finite element formulation for the boundary controllability of the wave equation, Internat. J. Numer. Methods Engrg., 27 (1989), 623-635.  doi: 10.1002/nme.1620270313. [15] R. Glowinski, C. H. Li and J.-L. Lions, A numerical approach to the exact boundary controllability of the wave equation. I. Dirichlet controls: Description of the numerical methods, Japan J. Appl. Math., 7 (1990), 1-76.  doi: 10.1007/BF03167891. [16] M. J. Grote, A. Schneebeli and D. Schötzau, Discontinuous Galerkin finite element method for the wave equation, SIAM J. Numer. Anal., 44 (2006), 2408-2431.  doi: 10.1137/05063194X. [17] P. Hansbo, Nitsche's method for interface problems in computational mechanics, GAMM-Mitt., 28 (2005), 183-206.  doi: 10.1002/gamm.201490018. [18] J. S. Hesthaven and R. M. Kirby, Filtering in Legendre spectral methods, Math. Comp., 77 (2008), 1425-1452.  doi: 10.1090/S0025-5718-08-02110-8. [19] J. A. Infante and E. Zuazua, Boundary observability for the space semi-discretizations of the $1$-D wave equation, M2AN Math. Model. Numer. Anal., 33 (1999), 407-438.  doi: 10.1051/m2an:1999123. [20] V. Komornik, Exact Controllability and Stabilization. The Multiplier Method, RAM: Research in Applied Mathematics, Masson, Paris; John Wiley & Sons, Ltd., Chichester, 1994. [21] I. Lasiecka, J.-L. Lions and R. Triggiani, Nonhomogeneous boundary value problems for second order hyperbolic operators, J. Math. Pures Appl., 65 (1986), 149-192. [22] I. Lasiecka and R. Triggiani, Regularity of hyperbolic equations under $L_{2}(0, \, T;L_{2}(\Gamma))$-Dirichlet boundary terms, Appl. Math. Optim., 10 (1983), 275-286.  doi: 10.1007/BF01448390. [23] I. Lasiecka and R. Triggiani, Exact controllability of the Euler-Bernoulli equation with controls in the Dirichlet and Neumann boundary conditions: A nonconservative case, SIAM J. Control Optim., 27 (1989), 330-373.  doi: 10.1137/0327018. [24] I. Lasiecka and R. Triggiani, Exact controllability of the wave equation with Neumann boundary control, Appl. Math. Optim., 19 (1989), 243-290.  doi: 10.1007/BF01448201. [25] I. Lasiecka and R. Triggiani, Differential and algebraic riccati equations with applications to boundary/point control problems: Continuous theory and approximation theory, in Lecture Notes in Control and Information Sciences, 164, Springer-Verlag, Berlin, 1991. doi: 10.1007/BFb0006880. [26] J.-L. Lions, Contrôlabilité exacte, perturbations et stabilisation de systèmes distribués. Tome 1, in Research in Applied Mathematics, 8, Masson, Paris, 1988. [27] A. Marica and E. Zuazua, Symmetric Discontinuous Galerkin Methods for 1-D Waves. Fourier Analysis, Propagation, Observability and Applications, SpringerBriefs in Mathematics, Springer, New York, 2014. doi: 10.1007/978-1-4614-5811-1. [28] M. Negreanu and E. Zuazua, Convergence of a multigrid method for the controllability of a 1-d wave equation, C. R. Math. Acad. Sci. Paris, 338 (2004), 413-418.  doi: 10.1016/j.crma.2003.11.032. [29] J. Nitsche, Über ein Variationsprinzip zur Lösung von Dirichlet-Problemen bei Verwendung von Teilräumen, die keinen Randbedingungen unterworfen sind, Abh. Math. Sem. Univ. Hamburg, 36 (1971), 9-15.  doi: 10.1007/BF02995904. [30] J. Shen, Efficient spectral-Galerkin method. I. Direct solvers of second- and fourth-order equations using Legendre polynomials, SIAM J. Sci. Comput., 15 (1994), 1489-1505.  doi: 10.1137/0915089. [31] R. Triggiani, Exact boundary controllability on ${L}_2({\Omega})\times {H}^{-1}({\Omega})$ of the wave equation with Dirichlet boundary control acting on a portion of the boundary $\partial\Omega$, and related problems, Appl. Math. Optim., 18 (1988), 241-277.  doi: 10.1007/BF01443625. [32] M. Tucsnak and G. Weiss, Observation and Control for Operator Semigroups, Birkhäuser Advanced Texts: Basler Lehrbücher, Birkhäuser Verlag, Basel, 2009. doi: 10.1007/978-3-7643-8994-9. [33] H. Vandeven, On the eigenvalues of second-order spectral differentiation operators, Comput. Methods Appl. Mech. Engrg., 80 (1990), 313-318.  doi: 10.1016/0045-7825(90)90035-K. [34] T. Warburton and J. S. Hesthaven, On the constants in $hp$-finite element trace inverse inequalities, Comput. Methods Appl. Mech. Engrg., 192 (2003), 2765-2773.  doi: 10.1016/S0045-7825(03)00294-9. [35] E. Zuazua, Boundary observability for the finite-difference space semi-discretizations of the 2-D wave equation in the square, J. Math. Pures Appl., 78 (1999), 523-563.  doi: 10.1016/S0021-7824(98)00008-7. [36] E. Zuazua, Propagation, observation, and control of waves approximated by finite difference methods, SIAM Rev., 47 (2005), 197-243.  doi: 10.1137/S0036144503432862.
Behaviour of the square roots of the discrete eigenvalues and of the continuous ones for $N = 40$
Behaviour of $c_{N, T}$ (left) and $C_{N, T}$ (right) with $T = 8$
Behaviour of $c_{N, T}$ (left) and $C_{N, T}$ (right) with $T = 8$} after Fourier filtering of order $M$, with $M$ the integer part of $\frac{2}{\pi}N$ \label{constfourier
Graphs of Cesàro, Lanczos, raised cosine and sharpened raised cosine filters
Graphs of Vandeven (left) and exponential (right) filters for different values of $p$
Values of $c_{N, T}$ (left column) and $C_{N, T}$ (right column) for different filters and $T = 8$. The exponential and Vandeven filters (bottom) are both of order $p = 4$
Values of $c_{N, T}$ (left) and $C_{N, T}$ (right) for the exponential filter with $p = 2$ and $T = 8$
Values of $c_{N, T}$ (left) and $C_{N, T}$ (right) associated to the mixed Legendre Galerkin formulation (23)-(24) with $T = 8$
Values of $c_{N, T}$ (left) and $C_{N, T}$ (right) with Nitsche's method, with $\gamma = 0.8$ and $T = 8$
Values of $c_{N, T}$ (left) and $C_{N, T}$ (right) for Nitsche's method, when the term $\gamma N^2u^N(1, t)$ is dropped in their definitions (27) and (28), with $\gamma = 0.8$ and $T = 8$
Numerical control $v^N(t)$ obtained with the Legendre Galerkin method (15) for $N = 32$ (top left) $N = 64$ (top right), $N = 128$ (bottom left) and $N = 256$ (bottom right). $T = 8$
Numerical controls with $N = 128$ with (from top to bottom): the classical formulation (15) (left), Exponential filtering (with p = 6) (right), the mixed formulation (left) and Nitsche's method (right)
Errors $|u_0^N-u_0|_{H^1_0}$, $\|u_1^N-u_1\|_{L^2}$ and $\|v^N-v\|_{L^2(0, T)}$ for the classical Legendre Galerkin method, and the remedies studied here : exponential spectral filtering (with p = 6), the mixed formulation and Nitsche's method ($\gamma = 1$), for $N = 32, \, 64, \, 128, \, 256$
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