Add force calculation kernel and fix incorrect ctest configuration for Cuda tests

kernels/forces.cu

@@ -0,0 +1,36 @@
+#include "forces.cuh"
+
+__global__ void CAC::calc_forces_and_energies(real *xs, real *forces,
+                                              real *energies, int n_particles,
+                                              real *box_len,
+                                              PairPotential &potential) {
+  int i = blockIdx.x * blockDim.x + threadIdx.x;
+  if (i < n_particles) {
+    real xi = xs[3 * i];
+    real yi = xs[3 * i + 1];
+    real zi = xs[3 * i + 2];
+
+    for (int j = 0; j < n_particles; j++) {
+      if (i != j) {
+        real xj = xs[3 * j];
+        real yj = xs[3 * j + 1];
+        real zj = xs[3 * j + 2];
+
+        real dx = xi - xj;
+        real dy = yi - yj;
+        real dz = zi - zj;
+
+        // Apply periodic boundary conditions
+        dx -= box_len[0] * round(dx / box_len[0]);
+        dy -= box_len[1] * round(dy / box_len[1]);
+        dz -= box_len[2] * round(dz / box_len[2]);
+
+        ForceAndEnergy sol = potential.calc_force_and_energy({dx, dy, dz});
+        forces[3 * i] += sol.force.x;
+        forces[3 * i + 1] += sol.force.y;
+        forces[3 * i + 2] += sol.force.z;
+        energies[i] = sol.energy;
+      }
+    }
+  }
+}