From ce74473eb06f23785117c91b1ef6e77090fc374c Mon Sep 17 00:00:00 2001
From: Amrita Goswami <amrita16thaug646@gmail.com>
Date: Sat, 23 Mar 2024 15:54:11 +0000
Subject: [PATCH] ActivityDrivenModel: Changed get_euler_slopes

We changed the definition of get_euler_slopes. Now the timestep is
multiplied in the update rule. This enables us to re-use
get_euler_slopes in the InertialModel.

Co-authored-by: Moritz Sallermann <moritzsallermann@gmail.com>
---
 include/models/ActivityDrivenModel.hpp |  6 +++---
 src/models/ActivityDrivenModel.cpp     | 10 ++++++----
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/include/models/ActivityDrivenModel.hpp b/include/models/ActivityDrivenModel.hpp
index 5cd4401..237bbe9 100644
--- a/include/models/ActivityDrivenModel.hpp
+++ b/include/models/ActivityDrivenModel.hpp
@@ -71,6 +71,7 @@ class ActivityDrivenModelAbstract : public Model<AgentT_>
     std::mt19937 & gen; // reference to simulation Mersenne-Twister engine
     std::set<std::pair<size_t, size_t>> reciprocal_edge_buffer{};
 
+protected:
     // Model-specific parameters
     double dt{}; // Timestep for the integration of the coupled ODEs
     // Various free parameters
@@ -93,7 +94,6 @@ class ActivityDrivenModelAbstract : public Model<AgentT_>
     double reluctance_eps{};
     double covariance_factor{};
 
-protected:
     size_t n_bots                     = 0; // The first n_bots agents are bots
     std::vector<int> bot_m            = std::vector<int>( 0 );
     std::vector<double> bot_activity  = std::vector<double>( 0 );
@@ -343,8 +343,8 @@ class ActivityDrivenModelAbstract : public Model<AgentT_>
                 k_buffer[idx_agent] += 1.0 / network.agents[idx_agent].data.reluctance * K * weight_buffer[j]
                                        * std::tanh( alpha * opinion( j_index ) );
             }
-            // Multiply by the timestep
-            k_buffer[idx_agent] *= dt;
+            // Here, we won't multiply by the timestep.
+            // Instead multiply in the update rule
         }
     }
 };
diff --git a/src/models/ActivityDrivenModel.cpp b/src/models/ActivityDrivenModel.cpp
index bdfc7c4..0b0dd9c 100644
--- a/src/models/ActivityDrivenModel.cpp
+++ b/src/models/ActivityDrivenModel.cpp
@@ -20,19 +20,21 @@ void ActivityDrivenModelAbstract<ActivityAgent>::iteration()
     get_euler_slopes( k1_buffer, [this]( size_t i ) { return network.agents[i].data.opinion; } );
     // k_2  =   hf(x_n+1/2h,y_n+1/2k_1)
     get_euler_slopes(
-        k2_buffer, [this]( size_t i ) { return network.agents[i].data.opinion + 0.5 * this->k1_buffer[i]; } );
+        k2_buffer, [this]( size_t i ) { return network.agents[i].data.opinion + 0.5 * dt * this->k1_buffer[i]; } );
     // k_3  =   hf(x_n+1/2h,y_n+1/2k_2)
     get_euler_slopes(
-        k3_buffer, [this]( size_t i ) { return network.agents[i].data.opinion + 0.5 * this->k2_buffer[i]; } );
+        k3_buffer, [this]( size_t i ) { return network.agents[i].data.opinion + 0.5 * dt * this->k2_buffer[i]; } );
     // k_4  =   hf(x_n+h,y_n+k_3)
-    get_euler_slopes( k4_buffer, [this]( size_t i ) { return network.agents[i].data.opinion + this->k3_buffer[i]; } );
+    get_euler_slopes(
+        k4_buffer, [this]( size_t i ) { return network.agents[i].data.opinion + dt * this->k3_buffer[i]; } );
 
     // Update the agent opinions
     for( size_t idx_agent = 0; idx_agent < network.n_agents(); ++idx_agent )
     {
         // y_(n+1) =   y_n+1/6k_1+1/3k_2+1/3k_3+1/6k_4+O(h^5)
         network.agents[idx_agent].data.opinion
-            += ( k1_buffer[idx_agent] + 2 * k2_buffer[idx_agent] + 2 * k3_buffer[idx_agent] + k4_buffer[idx_agent] )
+            += dt
+               * ( k1_buffer[idx_agent] + 2 * k2_buffer[idx_agent] + 2 * k3_buffer[idx_agent] + k4_buffer[idx_agent] )
                / 6.0;
     }