Add Phase 6.2: Computational Electromagnetics (Maxwell FDTD)

Chapter 16 implementing FDTD Maxwell's equations solver:

Source code (src/maxwell/):
- maxwell_devito.py: 1D and 2D FDTD solvers using Devito
- pml.py: Convolutional PML (CPML) absorbing boundaries
- sources.py: Gaussian, sinusoidal, Ricker wavelet sources
- analytical.py: Plane wave, cavity modes for verification

Chapter content (chapters/maxwell/):
- Maxwell's equations and curl form
- Yee grid staggered field placement
- Leapfrog time stepping and CFL stability
- Devito implementation patterns
- PEC, PMC, and ABC boundary conditions
- PML theory and implementation
- Examples: plane wave, resonant cavity, waveguide
- 10 exercises

Tests (55 new tests):
- Source functions and PML coefficients
- 1D/2D FDTD solver verification
- Energy conservation and CFL stability
- Boundary condition enforcement

References: Yee1966, Taflove2005, Berenger1994, Roden2000, Mur1981

Author: ggorman

_quarto.yml

@@ -29,6 +29,7 @@ book:
         - chapters/cfd/index.qmd
         - chapters/darcy/index.qmd
         - chapters/finance/index.qmd
+        - chapters/maxwell/index.qmd
     - part: "Appendices"
       chapters:
         - chapters/appendices/formulas/index.qmd
@@ -193,6 +194,7 @@ src_formulas: "https://github.com/devitocodes/devito_book/tree/devito/src/formul
 src_softeng2: "https://github.com/devitocodes/devito_book/tree/devito/src/softeng2"
 src_finance: "https://github.com/devitocodes/devito_book/tree/devito/src/finance"
 src_theory: "https://github.com/devitocodes/devito_book/tree/devito/src/theory"
+src_maxwell: "https://github.com/devitocodes/devito_book/tree/devito/src/maxwell"
 
 crossref:
   eq-prefix: ""

chapters/maxwell/index.qmd

@@ -0,0 +1,3 @@
+# Computational Electromagnetics {#sec-ch-maxwell}
+
+{{< include maxwell.qmd >}}