A comparative study on nonlocal diffusion operators related to the fractional Laplacian

Figure 1.  Comparison of the function ${\mathcal L}u$ with $u$ defined in (3.1), where the operator ${\mathcal L}$ represents ${\mathcal L}_s$ (solid line), ${\mathcal L}_h$ (dashed line), ${\mathcal L}_r$ (dash-dot line), or ${\mathcal L}_p$ with $\delta = 4$ (dotted line). For easy comparison, the result for ${\mathcal L} = -\partial_{xx}$ (line with symbols "^*") is included in the plot of $\alpha = 1.95$. For $\alpha = 1$, $1.5$ or $1.95$, the plots in $y$-direction are partially presented

Figure 2.  Difference between the peridynamic operator and the fractional Laplacian versus the parameter $\alpha $, where $u(x)$ is defined in (3.1)

Figure 3.  Comparison of the function ${\mathcal L}u$ with $u$ defined in (3.2) with $q = 2$. The operator ${\mathcal L}$ represents ${\mathcal L}_s$ (solid line), ${\mathcal L}_h$ (dashed line), ${\mathcal L}_r$ (dash-dot line), or ${\mathcal L}_p$ with $\delta = 4$ (dotted line).For easy comparison, the result for ${\mathcal L} = -\partial_{xx}$ (line with symbols "^*") is included in the plot of $\alpha = 1.95$

Figure 4.  Comparison of the function ${\mathcal L}u$ with $u$ defined in (3.2) with $q = 2$. The operator ${\mathcal L}$ represents ${\mathcal L}_s$ (solid line), ${\mathcal L}_h$ (dashed line), ${\mathcal L}_r$ (dash-dot line), or ${\mathcal L}_p$ with $\delta = 4$ (dotted line)

Figure 5.  Comparison of the function ${\mathcal L}u$ with $u$ defined in (3.2) with $q = 1$. The operator ${\mathcal L}$ represents ${\mathcal L}_s$ (solid line), ${\mathcal L}_h$ (dashed line), ${\mathcal L}_r$ (dash-dot line), or ${\mathcal L}_p$ with $\delta = 4$ (dotted line)

Figure 6.  The absolute (left panel) and relative (right panel) differences in the eigenvalues of the fractional Laplacian and the spectral fractional Laplacian

Figure 7.  The first (left panel) and second (right panel) eigenfunctions of the spectral fractional Laplacian ${\mathcal L}_s$ (solid line), fractional Laplacian ${\mathcal L}_h$ (dashed line), and regional fractional Laplacian ${\mathcal L}_r$ (dash-dot line). Note that the eigenfunctions of the spectral fractional Laplacian ${\mathcal L}_s$ are independent of $\alpha > 0$

Figure 8.  Comparison of the solution to (3.4) with ${\mathcal L}_s$ (solid line), ${\mathcal L}_h$ (dashed line), ${\mathcal L}_r$ (dash-dot line), or ${\mathcal L}_p$ with $\delta = 4$ (dotted line). For easy comparison, the result for ${\mathcal L} = -\partial_{xx}$ (line with symbols "^*") is included in the plot of $\alpha = 1.95$

Figure 9.  Effects of the horizon size $\delta $ on the solution of the nonlocal problem (3.4) with the peridynamic operator ${\mathcal L}_p$, where $\delta = 2$ (solid line), $1$ (dash-dot line), or $0.5$ (dashed line)

Figure 10.  Time evolution of the solution $u(x, t)$ to the nonlocal diffusion equation (3.6) with ${\mathcal L}_s$ (upper row), ${\mathcal L}_h$ (middle row), and ${\mathcal L}_r$ (lower row)

Figure 11.  Time evolution of the solution $u(x, t)$ to the nonlocal diffusion equation (3.6) with the peridynamic operator ${\mathcal L}_p$, where the horizon size $\delta = 0.1$ (top) or $\delta = 1$ (bottom)

Figure 12.  Solutions of the nonlocal diffusion equation (3.6) at time $t = 0.1, 0.5, 1$, where the operator is chosen as ${\mathcal L}_s$ (solid line), ${\mathcal L}_h$ (dashed line), ${\mathcal L}_p$ (dotted line), or ${\mathcal L}_r$ (dash-dot line). For easy comparison, we include the solution of the classical diffusion equation (i.e., ${\mathcal L}_i = -\partial_{xx}$ in (3.6)) in the last row

Figure 13.  Time evolution of the solution $u(x, t)$ to the nonlocal diffusion-reaction equation (3.10) with ${\mathcal L}_s$ (row one), ${\mathcal L}_h$ (row two), and ${\mathcal L}_r$ (row three)

Figure 14.  Time evolution of the solution $u(x, t)$ to the nonlocal diffusion-reaction equation (3.6) with the peridynamic operator ${\mathcal L}_p$, where the horizon size $\delta = 0.1$ (top) or $\delta = 0.5$ (bottom)

Figure 15.  Solutions of the nonlocal diffusion-reaction equation (3.10) at time $t = 0.1, 0.5, 1$, where the operator is chosen as ${\mathcal L}_s$ (solid line), ${\mathcal L}_h$ (dashed line), ${\mathcal L}_p$ (dotted line), or ${\mathcal L}_r$ (dash-dot line). For easy comparison, we include the solution of the classical diffusion equation (i.e., ${\mathcal L}_i = -\partial_{xx}$ in (3.10)) in the last row