feat: add support for dynamically varying algorithm paramters

include/swarm.hpp

@@ -12,7 +12,7 @@ struct Agent {
     using F = std::function<float(T)>;
 
     virtual void move(float dt) = 0;
-    virtual void step(float dt) = 0;
+    virtual void step() = 0;
 
     virtual std::pair<float, T> best() const = 0;
 
@@ -21,44 +21,87 @@ protected:
     F f;
 };
 
-template<std::size_t N>
+template <typename A>
+concept ParameterChangeAlgorithm = requires(A alg, float f, unsigned int i) {
+    { alg(f, f, f, i, i) } -> std::same_as<vec<3>>;
+};
+
+namespace ParamChange {
+    struct Const {
+	vec<3> operator()(
+	    float visc, float nostal, float peerp, int _1, int _2) {
+	    return {visc, nostal, peerp};
+	}
+    };
+
+    struct MLinAlg {
+	vec<3> operator()(
+	    float visc, float nostal, float peerp, int curr, int max) {
+	    float pct_done = (float)curr / (float)max;
+	    return {
+		visc   - (0.9f - 0.4f) * pct_done,
+		nostal - (2.5f - 0.5f) * pct_done,
+		peerp  + (2.5f - 0.5f) * pct_done,
+	    };
+	}
+    };
+};
+
+template<std::size_t N, ParameterChangeAlgorithm A = ParamChange::MLinAlg>
 struct Particle : public Agent<vec<N>> {
     std::pair<float, vec<N>> best() const override { return {pb, pb_pos}; };
 
     void move(float dt=1) override { position = position + velocity * dt; }
 
-    void step(float dt=1) override {
-	velocity = kviscosity * velocity
-	    + knostalgia * (pb_pos - position)
-	    + kpeer_pressure * (peer.best().second - position);
+    void step() override {
+	velocity = viscosity * velocity
+	    + nostalgia * (pb_pos - position)
+	    + peer_pressure * (peer.best().second - position);
 
 	float y = f(position);
 	if(y < pb) {
 	    pb = y;
 	    pb_pos = position;
 	}
+
+	vec<3> params = alg(kviscosity, knostalgia, kpeer_pressure,
+			    curr_iter, max_iter);
+
+	viscosity = params.x;
+	nostalgia = params.y;
+	peer_pressure = params.z;
+
+	curr_iter++;
     };
 
-    float kviscosity = 0.9f;
-    float knostalgia = 2.5f;
-    float kpeer_pressure = 0.5f;
+    const float kviscosity = 0.9f;
+    const float knostalgia = 2.5f;
+    const float kpeer_pressure = 0.5f;
+
+    float viscosity = kviscosity;
+    float nostalgia = knostalgia;
+    float peer_pressure = kpeer_pressure;
 
     Particle(Agent<vec<N>>::F f, const Agent<vec<N>>& peer,
-	     vec<N> position, vec<N> velocity)
+	     vec<N> position, vec<N> velocity, unsigned max_iter)
 	: Agent<vec<N>>(f), position(position), velocity(velocity),
-	  pb_pos(position), peer(peer) {
+	  pb_pos(position), max_iter(max_iter), peer(peer) {
 	pb = f(position);
     }
 
     const vec<N> &get_position() const { return position; };
 
 private:
+    A alg;
     vec<N> position;
     vec<N> velocity;
 
     vec<N> pb_pos;
     float pb;
 
+    unsigned curr_iter = 0;
+    unsigned max_iter;
+
     const Agent<vec<N>>& peer;
 };
 
@@ -71,7 +114,7 @@ struct Swarm : public Agent<vec<N>> {
 	    p.move(dt);
     }
 
-    void step(float dt=1) override {
+    void step() override {
 	if(particles.empty()) return;
 
 	// find best before step() on each particle
@@ -85,26 +128,28 @@ struct Swarm : public Agent<vec<N>> {
 	best_pos = b->best().second;
 
 	for(auto &p : particles)
-	    p.step(dt);
+	    p.step();
     }
 
     void add_particle(std::size_t n=1) {
 	for(std::size_t i=0; i <= n; ++i)
 	    particles.push_back(
-		Particle<N>(this->_f, *this, vec<N>(0), vec<N>(10))
+		Particle<N>(this->_f, *this, vec<N>(0), vec<N>(10), max_iter)
 	    );
     }
 
     void add_particle(const vec<N> &pos, const vec<N> &vel) {
 	particles.push_back(
-	    Particle<N>(this->f, *this, pos, vel)
+	    Particle<N>(this->f, *this, pos, vel, max_iter)
 	);
     }
 
     const std::vector<Particle<N>>& get_particles() { return particles; };
 
-    Swarm(Agent<vec<N>>::F f) : Agent<vec<N>>(f) {}
+    Swarm(Agent<vec<N>>::F f, unsigned max_iter = 150)
+	: Agent<vec<N>>(f), max_iter(max_iter) {}
 private:
+    unsigned max_iter;
     vec<N> best_pos;
     float best_val;
     std::vector<Particle<N>> particles;

src/main.cpp

@@ -8,8 +8,8 @@ static constexpr int   kFPS = 60;
 static constexpr float kDT  = 1.0 / kFPS;
 
 float f(vec<2> x) {
-    return 50 * (std::pow(std::sin((x.x - 10)/2),2) + std::pow(std::sin(x.y/2),2))
-	+ std::pow(std::abs(x.x - 10), 1.2) + std::pow(std::abs(x.y), 1.2);
+    return  50 * (std::pow(std::sin((x.x - 10)/2),2) + std::pow(std::sin(x.y/2),2)) +
+	std::pow(std::abs(x.x - 3.141592653589), 1.2) + std::pow(std::abs(x.y), 1.2);
 }
 
 int
@@ -18,7 +18,7 @@ main(int argc, char **argv) {
     if(argc < 2) iter_count = 100;
     else sscanf(argv[1], "%d", &iter_count);
 
-    Swarm<2> swarm(f);
+    Swarm<2> swarm(f, iter_count);
     Screen scr(80, 24);
 
     TanhColorizer tanh_col;
@@ -148,7 +148,7 @@ main(int argc, char **argv) {
 
 	case 'p':
 	    auto [y, x] = swarm.best();
-	    printf("Current best: f(%.3f, %.3f) = %.3f", x.x, x.y, y);
+	    printf("Current best: f(%.10f, %.10f) = %.10f", x.x, x.y, y);
 	    break;
 	}