WIP: re-introduction virtual sites at COM

[mebrito]

Fixes #4619

Description of changes:

• implement new type of virtual site

[espresso-ci]

Your pull request does not meet our code formatting rules. Specifically, I suggest you make the following changes:

diff --git a/src/core/virtual_sites/CMakeLists.txt b/src/core/virtual_sites/CMakeLists.txt
index 10020fc52..b94e675a4 100644
--- a/src/core/virtual_sites/CMakeLists.txt
+++ b/src/core/virtual_sites/CMakeLists.txt
@@ -23,4 +23,4 @@ target_sources(
           ${CMAKE_CURRENT_SOURCE_DIR}/lb_inertialess_tracers_cuda_interface.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/VirtualSitesInertialessTracers.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/VirtualSitesRelative.cpp
-	  ${CMAKE_CURRENT_SOURCE_DIR}/VirtualSitesCenterOfMass.cpp)
+          ${CMAKE_CURRENT_SOURCE_DIR}/VirtualSitesCenterOfMass.cpp)
diff --git a/src/core/virtual_sites/VirtualSitesCenterOfMass.cpp b/src/core/virtual_sites/VirtualSitesCenterOfMass.cpp
index 24c6e6a65..c1da295fd 100644
--- a/src/core/virtual_sites/VirtualSitesCenterOfMass.cpp
+++ b/src/core/virtual_sites/VirtualSitesCenterOfMass.cpp
@@ -23,12 +23,12 @@
 
 #include "Particle.hpp"
 #include "cells.hpp"
+#include "communication.hpp"
 #include "errorhandling.hpp"
 #include "forces.hpp"
 #include "grid.hpp"
 #include "integrate.hpp"
 #include "rotation.hpp"
-#include "communication.hpp"
 
 #include <utils/Vector.hpp>
 #include <utils/math/quaternion.hpp>
@@ -101,12 +101,13 @@ void VirtualSitesCenterOfMass::back_transfer_forces() {
   // cell_structure.ghosts_reduce_forces();
   // init_forces_ghosts(cell_structure.ghost_particles());
 
-  //int p_mol_id;
-  //int vs_id;
+  // int p_mol_id;
+  // int vs_id;
   for (auto &p : cell_structure.local_particles()) {
-    //p_mol_id = p.mol_id();
-    //vs_id = vitual_site_id_for_mol_id[p.mol_id()];
-    auto vs_ptr = cell_structure.get_local_particle(vitual_site_id_for_mol_id[p.mol_id()]);
+    // p_mol_id = p.mol_id();
+    // vs_id = vitual_site_id_for_mol_id[p.mol_id()];
+    auto vs_ptr = cell_structure.get_local_particle(
+        vitual_site_id_for_mol_id[p.mol_id()]);
     p.force() +=
         (p.mass() / com_by_mol_id[p.mol_id()]->total_mass) * vs_ptr->force();
   }
diff --git a/src/core/virtual_sites/VirtualSitesCenterOfMass.hpp b/src/core/virtual_sites/VirtualSitesCenterOfMass.hpp
index 5a719f964..df8d8e709 100644
--- a/src/core/virtual_sites/VirtualSitesCenterOfMass.hpp
+++ b/src/core/virtual_sites/VirtualSitesCenterOfMass.hpp
@@ -39,8 +39,8 @@
  *  - update virtual sites
  */
 
-#include <iostream>
 #include "config/config.hpp"
+#include <iostream>
 
 //#ifndef VIRTUAL_SITES_CENTER_OF_MASS
 
@@ -53,8 +53,8 @@
 /** @brief Base class for virtual sites implementations */
 class VirtualSitesCenterOfMass : public VirtualSites {
 public:
-  VirtualSitesCenterOfMass(const std::unordered_map<int, int> & mid_for_vs) : 
-    vitual_site_id_for_mol_id(mid_for_vs) {}
+  VirtualSitesCenterOfMass(const std::unordered_map<int, int> &mid_for_vs)
+      : vitual_site_id_for_mol_id(mid_for_vs) {}
   /**
    * @brief Update positions and velocities of virtual sites.
    */
@@ -67,8 +67,9 @@ public:
   std::unordered_map<int, int> vitual_site_id_for_mol_id = {};
 
   auto const &get_mid_for_vs() const { return vitual_site_id_for_mol_id; }
-  
-  void set_mid_for_vs( std::unordered_map<int, int> const &vitual_site_id_for_mol_id_ ) {
+
+  void set_mid_for_vs(
+      std::unordered_map<int, int> const &vitual_site_id_for_mol_id_) {
     vitual_site_id_for_mol_id = vitual_site_id_for_mol_id_;
   }
 
diff --git a/src/script_interface/virtual_sites/VirtualSitesCenterOfMass.hpp b/src/script_interface/virtual_sites/VirtualSitesCenterOfMass.hpp
index 5c839dafb..057e29949 100644
--- a/src/script_interface/virtual_sites/VirtualSitesCenterOfMass.hpp
+++ b/src/script_interface/virtual_sites/VirtualSitesCenterOfMass.hpp
@@ -30,28 +30,28 @@
 
 #include "core/virtual_sites/VirtualSitesCenterOfMass.hpp"
 
-#include <memory>
 #include <map>
+#include <memory>
 
 namespace ScriptInterface {
 namespace VirtualSites {
 
 class VirtualSitesCenterOfMass : public VirtualSites {
 public:
-
   void do_construct(VariantMap const &args) override {
-    auto mid_for_vs = get_value<std::unordered_map<int, int>>(args, "mid_for_vs");
+    auto mid_for_vs =
+        get_value<std::unordered_map<int, int>>(args, "mid_for_vs");
     m_virtual_sites = std::make_shared<::VirtualSitesCenterOfMass>(mid_for_vs);
 
-    add_parameters({
-        {"mid_for_vs", AutoParameter::read_only,
-         [this]() { return make_unordered_map_of_variants(m_virtual_sites->get_mid_for_vs()); }}
-    });
+    add_parameters({{"mid_for_vs", AutoParameter::read_only, [this]() {
+                       return make_unordered_map_of_variants(
+                           m_virtual_sites->get_mid_for_vs());
+                     }}});
   }
 
   std::shared_ptr<::VirtualSites> virtual_sites() override {
     return m_virtual_sites;
-      } 
+  }
 
 private:
   std::shared_ptr<::VirtualSitesCenterOfMass> m_virtual_sites;
diff --git a/src/script_interface/virtual_sites/initialize.cpp b/src/script_interface/virtual_sites/initialize.cpp
index c1a5c3181..1158d4952 100644
--- a/src/script_interface/virtual_sites/initialize.cpp
+++ b/src/script_interface/virtual_sites/initialize.cpp
@@ -21,10 +21,10 @@
 #include "initialize.hpp"
 
 #include "ActiveVirtualSitesHandle.hpp"
+#include "VirtualSitesCenterOfMass.hpp"
 #include "VirtualSitesInertialessTracers.hpp"
 #include "VirtualSitesOff.hpp"
 #include "VirtualSitesRelative.hpp"
-#include "VirtualSitesCenterOfMass.hpp"
 
 namespace ScriptInterface {
 namespace VirtualSites {
@@ -40,7 +40,8 @@ void initialize(Utils::Factory<ObjectHandle> *om) {
   om->register_new<VirtualSitesRelative>("VirtualSites::VirtualSitesRelative");
 #endif
 #ifdef VIRTUAL_SITES_CENTER_OF_MASS
-  om->register_new<VirtualSitesCenterOfMass>("VirtualSites::VirtualSitesCenterOfMass");
+  om->register_new<VirtualSitesCenterOfMass>(
+      "VirtualSites::VirtualSitesCenterOfMass");
 #endif
   om->register_new<ActiveVirtualSitesHandle>(
       "VirtualSites::ActiveVirtualSitesHandle");

To apply these changes, please do one of the following:

• You can download a patch with my suggested changes here, inspect it and make changes manually.
• You can directly apply it to your repository by running curl https://gitlab.icp.uni-stuttgart.de/espressomd/espresso/-/jobs/356150/artifacts/raw/style.patch | git apply -.
• You can run maintainer/CI/fix_style.sh to automatically fix your coding style. This is the same command that I have executed to generate the patch above, but it requires certain tools to be installed on your computer.

You can run gitlab-runner exec docker style afterwards to check if your changes worked out properly.

Please note that there are often multiple ways to correctly format code. As I am just a robot, I sometimes fail to identify the most aesthetically pleasing way. So please look over my suggested changes and adapt them where the style does not make sense.