From 718a275bcf132f1e0efe4d0bfec070839739604c Mon Sep 17 00:00:00 2001
From: Miikka Vaisala <mvaisala@asiaa.sinica.edu.tw>
Date: Thu, 1 Aug 2019 14:12:21 +0800
Subject: [PATCH] Proiper softening factor

---
 acc/mhd_solver/stencil_process.sps | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/acc/mhd_solver/stencil_process.sps b/acc/mhd_solver/stencil_process.sps
index a4970b5..0d47dad 100644
--- a/acc/mhd_solver/stencil_process.sps
+++ b/acc/mhd_solver/stencil_process.sps
@@ -69,7 +69,8 @@ sink_gravity(int3 globalVertexIdx){
                               DCONST_REAL(AC_sink_pos_y),
                               DCONST_REAL(AC_sink_pos_z)}; 
     const Scalar distance = length(grid_pos - sink_pos);
-    const Scalar gravity_magnitude = (Scalar(0.01) * sink_mass) / (distance * distance);
+    const Scalar soft = 0.12;
+    const Scalar gravity_magnitude = (Scalar(0.01) * sink_mass) / pow(((distance * distance) +  soft*soft), 1.5);
     const Vector direction = (Vector){(sink_pos.x - grid_pos.x) / distance,
                                       (sink_pos.y - grid_pos.y) / distance,
                                       (sink_pos.z - grid_pos.z) / distance};