nufi, still need to marry with deal.ii s poisson

nufi_solver.hpp

@@ -0,0 +1,133 @@
+#ifndef NUFI_SOLVER_HPP
+#define NUFI_SOLVER_HPP
+
+#include <deal.II/base/point.h>
+#include <deal.II/base/tensor.h>
+#include <deal.II/numerics/fe_field_function.h>
+
+#include <vector>
+#include <cstddef>
+
+#include "parameters.hpp"
+#include "poisson_problem.hpp"
+#include "fields.hpp" // holds f0(x,v), and compute_rho(x)
+
+using namespace dealii;
+
+class NuFISolver
+{
+public:
+  NuFISolver();
+
+  void run();
+  double eval_rho(size_t n, double x, double u);
+
+private:
+
+  void compute_density();
+  void solve_poisson();
+  void update_distribution();
+
+  double evaluate_E(double x);
+
+  PoissonProblem<1> poisson;
+
+  std::vector<double> coeffs;
+  std::vector<double> rho;
+
+  unsigned int Nt;
+  unsigned int Nx;
+
+  double Lx = Parameters::LX;
+
+  unsigned int order;
+
+  double dt;
+  size_t stride_t;
+};
+
+inline double NuFISolver::evaluate_E(double x)
+{
+  // Wrap x into the periodic domain
+  double x_periodic = x - Lx * std::floor(x / Lx);
+  Point<1> p(x_periodic);
+
+  Functions::FEFieldFunction<1> E_field(
+        poisson.get_dof_handler(),
+        poisson.get_solution()
+    );
+
+  double E_val = 0.0;
+
+  try
+  {
+      // Evaluate the electric field at point p
+      // If your solution represents phi, take negative gradient
+      Tensor<1,1> grad = E_field.gradient(p);
+      E_val = -grad[0];  // -∂φ/∂x
+  }
+  catch (const VectorTools::ExcPointNotAvailableHere &)
+  {
+      // This happens if p lies in an artificial cell in parallel
+      AssertThrow(false, ExcMessage("Point not available on this process."));
+  }
+
+  return E_val;
+}
+
+inline double NuFISolver::eval_rho(size_t n,
+                                      double x,
+                                      double u)
+{
+    if (n == 0)
+        return f0(x,u);
+   
+    double Ex;
+
+    // Initial half-step.
+    Ex = evaluate_E(x);
+    u += 0.5*dt*Ex;
+
+    while ( --n )
+    {
+        x -= dt*u;
+        Ex = evaluate_E(x);
+        u += dt*Ex;
+    }
+
+    // Final half-step.
+    x -= dt*u;
+    Ex = evaluate_E(x);
+    u += 0.5*dt*Ex; // is this line useless ?
+    
+    double x_periodic = x - Lx * std::floor(x / Lx);
+
+    return compute_rho(x_periodic); // compute_rho (from fields.hpp) uses f0
+}
+
+inline void NuFISolver::run()
+{
+    rho.resize(Nx, 0.0);               // initialize density array
+
+    // Main time-stepping loop
+    for (size_t n = 0; n < Nt; ++n)
+    {
+
+        // Solve this logic! To use on deal.ii  
+
+        // 1. Compute charge density rho from current distribution
+        compute_density();
+
+        // 2. Solve Poisson's equation to update electric field
+        solve_poisson();
+
+        // 3. Update distribution function along characteristics
+        update_distribution();
+
+        // Optional: compute ftilda at current step if needed
+        // for demonstration: evaluate ftilda at midpoint x, u = 0
+        // double ft = eval_ftilda(n, 0.5 * poisson.get_Lx(), 0.0);
+    }
+}
+
+#endif