1 files changed, 118 insertions, 0 deletions
diff --git a/code/core/synapse.cpp b/code/core/synapse.cpp
new file mode 100644
index 0000000..cc7399a
--- /dev/null
+++ b/code/core/synapse.cpp
@@ -0,0 +1,118 @@
+#include <math.h>
+
+#include "synapse.h"
+
+Synapse::Synapse() :
+  src(-1), dst(-1), // seeing this value indicates an unused synapse
+  weight(0.0),
+  eligibility(0.0),
+  delay(0.0),
+  constant(false),
+  firstSpike(- INFINITY),
+  lastSpike(- INFINITY),
+  evolvedUntil(0.0)
+{}
+
+// given an input time and current calculate their output values
+void Synapse::computePostsynapticPulse(double &time, double &current) {
+  time += delay;
+  current = weight;
+}
+
+void Synapse::evolve(double time) {
+  if (time < evolvedUntil)
+    return;
+
+  // get the dopamin history starting from a dopamin event earlier than the synpase's last event
+  std::list<pair<double, double> >::iterator i = s.da_history.begin();
+  while (i->first > evolvedUntil)
+    i++;
+
+  // evolve synapse state for each interval given by the dopamin history
+  while (evolvedUntil < time) {
+    double da_level = i->second;
+    if (i->first < evolvedUntil) // the first dopamin event partially lies outside our time window
+      da_level = g.decay_dopamin(da_level, evolvedUntil - i->first);
+
+    double td = - evolvedUntil;
+    if (i == s.da_history.begin()) {
+      // this is the last (=newest) element of the history
+      td += time;
+      evolvedUntil = time;
+    }else{
+      i--;
+      if (i->first > time) {
+	// dopamin history goes furher (in time) than we have to simulate
+	td += time;
+	evolvedUntil = time;
+      }else{
+	td += i->first;
+	evolvedUntil += td;
+      }
+    }
+
+    /* below is the exact solution of the equation system
+         dc/dt = -Cc          c - eligibility trace, C - cf. tau
+         dd/dt = -Dd          d - dopamin level, D - cf. tau
+         dw/dt = cd           w - weight
+    */
+    
+    if (!constant) {
+      double tau = g.dopamin_tau * g.stdp_et_tau / (g.dopamin_tau + g.stdp_et_tau);
+      double dw = da_level * eligibility * tau * (1 - exp( -td / tau ));
+      weight += dw;
+      weight = fmax( msg.Wmin, fmin( msg.Wmax, weight ));
+    }
+    eligibility *= exp( -td / g.stdp_et_tau );
+  }
+}
+
+// modify eligibility trace according to a single STDP event given by
+// a pre-post time difference (= t_post - t_pre)
+void Synapse::stdp(double td) {
+  if (td >= 0.0) {// WARN: this doesn't work with negative zero
+    eligibility = g.stdp_lambda_plus * exp( - td / g.stdp_tau_plus );
+  }else{
+    eligibility = - g.stdp_lambda_minus * exp( td / g.stdp_tau_minus );
+  }
+}
+
+static void Synapse::updateTopology() {
+  // clear the sin/sout lists of all neurons
+  for (int i=0; i<numNeurons; i++) {
+    n[i].sout.clear();
+    n[i].sin.clear();
+  }
+
+  // iterate over all synapses wich have a valid source and destination (neuron) and add them to sin/sout lists
+  int i;
+  for (i=0; (i<maxSynapses) && (syn[i].src != -1) && (syn[i].dst != -1); i++) {
+    n[syn[i].src].sout.push_front(syn[i]);
+    n[syn[i].dst].sin.push_front(syn[i]);
+  }
+
+  // store number of (used) synapses
+  numSynapses = i;
+}
+
+template<class Action>
+bool Synapse::reflect<Action>(Action &a) {
+  return
+    a(src, "src")
+    && a(dst, "dst")
+    && a(weight, "weight")
+    && a(eligibility, "eligibility")
+    && a(delay, "delay")
+    && a(constant, "constant")
+    && a(firstSpike, "firstSpike")
+    && a(lastSpike, "lastSpike")
+    && a(evolvedUntil, "evolvedUntil");
+}
+
+static id_type Synapse::numElements() {
+  return numSynapsesDec;
+}
+
+static Synapse * Synapse::singleton(id_type id) {
+  return &(synapses[id]);
+}