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We consider a nonlocal approximation of the quadratic porous medium equation where the pressure is given by a convolution with a mollification kernel. It is known that when the kernel concentrates around the origin, the nonlocal equation converges to the local one. In one spatial dimension, for a particular choice of the kernel, and under mere assumptions on the initial condition, we quantify the rate of convergence in the 2-Wasserstein distance. Our proof is very simple, exploiting the so-called evolutionary variational inequality for both the nonlocal and local equations as well as a priori estimates. We also present numerical simulations using the finite volume method, which suggests that the obtained rate can be improved; this will be addressed in a forthcoming work.
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Figure 2. Porous medium equation versus blob method: Order of convergence for $ \mathcal{W}_2( u_{\varepsilon}, u_0) $, $ u_0 $ solution of (1.3), and $ u_{\varepsilon} $ solution of (1.1). The computational domain is $ \Omega = (-10, 10) $, $ u^0(x) = (1/\sqrt{2\pi}) \exp(-|x|^2/2) $ is the initial datum, and a uniform grid of $ N = 2^{12} $ cells was used with $ \Delta t = 0.01 $
Figure 3. Porous medium equation and blob method: Order of convergence for $ \mathcal{W}_2( u_{\varepsilon}, u_0) $, $ u_0 $ solution of (1.3), and $ u_{\varepsilon} $ solution of (1.1). The computational domain $ \Omega = (-3, 3) $, $ u^0(x) = (1-x^2)_+ $ is the initial datum, a uniform grid of $ N = 2^{10} $ cells with $ \Delta t = 0.01 $ was used, periodic boundary conditions were imposed
Figure 4. Porous medium equation and blob method: Order of convergence for $ \mathcal{W}_2( u_{\varepsilon}, u_0) $, $ u_0 $ solution of (1.3), and $ u_{\varepsilon} $ solution of (1.1). The computational domain is $ \Omega = (-3, 3) $, $ u^0(x) = (1-x^2)_+ $ is the initial datum, a uniform grid of $ N = 2^{10} $ cells was used with $ \Delta t = 0.01 $, and no-flux boundary conditions were imposed
Figure 5. Porous medium Fokker-Planck equation and blob method: order of convergence for $ \mathcal{W}_2( u_{\varepsilon}, u_0) $, $ u_0 $ solution of (3.6), and $ u_{\varepsilon} $ solution of (3.7). The computational domain is $ \Omega = (-20, 20) $, $ u^0(x) = 1/|\Omega| + 10 $ is the initial datum, and a uniform grid of $ N = 2^{13} $ cells was used with $ \Delta t = 0.01 $
Figure 6. Porous medium equation and blob method: Order of convergence for $ \mathcal{W}_2( u_{\varepsilon}, u_0) $, $ u_0 $ (solution of (3.6)), and $ u_{\varepsilon} $ (solution of (3.7)). The computational domain is $ \Omega = (-10, 10) $, $ u^0(x) = u(x, 0) $, a the initial datum is generated using random values on a uniform grid of $ N = 2^{12} $ cells, with $ \Delta t = 0.01 $
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Finite-Volume scheme: size of cells and
Porous medium equation versus blob method: Order of convergence for
Porous medium equation and blob method: Order of convergence for
Porous medium equation and blob method: Order of convergence for
Porous medium Fokker-Planck equation and blob method: order of convergence for
Porous medium equation and blob method: Order of convergence for
Porous medium equation and blob method: