Fix bug in elastic.cu: adjoint pressure injection was missing division by 2

Author: ar4

src/deepwave/elastic.cu

@@ -108,8 +108,8 @@ __global__ void add_adjoint_pressure_sources(
   if (source_idx < n_receivers_p_per_shot && shot_idx < n_shots) {
     int64_t k = shot_idx * n_receivers_p_per_shot + source_idx;
     if (0 <= sources_i[k]) {
-      sigmayy[shot_idx * nynx + sources_i[k]] -= f[k];
-      sigmaxx[shot_idx * nynx + sources_i[k]] -= f[k];
+      sigmayy[shot_idx * nynx + sources_i[k]] -= f[k] / (DW_DTYPE)2;
+      sigmaxx[shot_idx * nynx + sources_i[k]] -= f[k] / (DW_DTYPE)2;
     }
   }
 }