From 8aa29810bb77611cc20b7a384897ff6703783ea1 Mon Sep 17 00:00:00 2001
From: Chris Dyer <cdyer@allegro.clab.cs.cmu.edu>
Date: Sun, 18 Nov 2012 13:35:42 -0500
Subject: major restructure of the training code

---
 training/utils/online_optimizer.h | 129 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 129 insertions(+)
 create mode 100644 training/utils/online_optimizer.h

(limited to 'training/utils/online_optimizer.h')

diff --git a/training/utils/online_optimizer.h b/training/utils/online_optimizer.h
new file mode 100644
index 00000000..28d89344
--- /dev/null
+++ b/training/utils/online_optimizer.h
@@ -0,0 +1,129 @@
+#ifndef _ONL_OPTIMIZE_H_
+#define _ONL_OPTIMIZE_H_
+
+#include <tr1/memory>
+#include <set>
+#include <string>
+#include <cmath>
+#include "sparse_vector.h"
+
+struct LearningRateSchedule {
+  virtual ~LearningRateSchedule();
+  // returns the learning rate for the kth iteration
+  virtual double eta(int k) const = 0;
+};
+
+// TODO in the Tsoruoaka et al. (ACL 2009) paper, they use N
+// to mean the batch size in most places, but it doesn't completely
+// make sense to me in the learning rate schedules-- this needs
+// to be worked out to make sure they didn't mean corpus size
+// in some places and batch size in others (since in the paper they
+// only ever work with batch sizes of 1)
+struct StandardLearningRate : public LearningRateSchedule {
+  StandardLearningRate(
+      size_t batch_size,        // batch size, not corpus size!
+      double eta_0 = 0.2) :
+    eta_0_(eta_0),
+    N_(static_cast<double>(batch_size)) {}
+
+  virtual double eta(int k) const;
+
+ private:
+  const double eta_0_;
+  const double N_;
+};
+
+struct ExponentialDecayLearningRate : public LearningRateSchedule {
+  ExponentialDecayLearningRate(
+      size_t batch_size,        // batch size, not corpus size!
+      double eta_0 = 0.2,
+      double alpha = 0.85       // recommended by Tsuruoka et al. (ACL 2009)
+    ) : eta_0_(eta_0),
+        N_(static_cast<double>(batch_size)),
+        alpha_(alpha) {
+    assert(alpha > 0);
+    assert(alpha < 1.0);
+  }
+
+  virtual double eta(int k) const;
+
+ private:
+  const double eta_0_;
+  const double N_;
+  const double alpha_;
+};
+
+class OnlineOptimizer {
+ public:
+  virtual ~OnlineOptimizer();
+  OnlineOptimizer(const std::tr1::shared_ptr<LearningRateSchedule>& s,
+                  size_t batch_size,
+                  const std::vector<int>& frozen_feats = std::vector<int>())
+      : N_(batch_size),schedule_(s),k_() {
+    for (int i = 0; i < frozen_feats.size(); ++i)
+      frozen_.insert(frozen_feats[i]);
+  }
+  void ResetEpoch() { k_ = 0; ResetEpochImpl(); }
+  void UpdateWeights(const SparseVector<double>& approx_g, int max_feat, SparseVector<double>* weights) {
+    ++k_;
+    const double eta = schedule_->eta(k_);
+    UpdateWeightsImpl(eta, approx_g, max_feat, weights);
+  }
+
+ protected:
+  virtual void ResetEpochImpl();
+  virtual void UpdateWeightsImpl(const double& eta, const SparseVector<double>& approx_g, int max_feat, SparseVector<double>* weights) = 0;
+  const size_t N_; // number of training instances per batch
+  std::set<int> frozen_;  // frozen (non-optimizing) features
+
+ private:
+  std::tr1::shared_ptr<LearningRateSchedule> schedule_;
+  int k_;  // iteration count
+};
+
+class CumulativeL1OnlineOptimizer : public OnlineOptimizer {
+ public:
+  CumulativeL1OnlineOptimizer(const std::tr1::shared_ptr<LearningRateSchedule>& s,
+                              size_t training_instances, double C,
+                              const std::vector<int>& frozen) :
+    OnlineOptimizer(s, training_instances, frozen), C_(C), u_() {}
+
+ protected:
+  void ResetEpochImpl() { u_ = 0; }
+  void UpdateWeightsImpl(const double& eta, const SparseVector<double>& approx_g, int max_feat, SparseVector<double>* weights) {
+    u_ += eta * C_ / N_;
+    for (SparseVector<double>::const_iterator it = approx_g.begin(); 
+         it != approx_g.end(); ++it) {
+      if (frozen_.count(it->first) == 0)
+        weights->add_value(it->first, eta * it->second);
+    }
+    for (int i = 1; i < max_feat; ++i)
+      if (frozen_.count(i) == 0) ApplyPenalty(i, weights);
+  }
+
+ private:
+  void ApplyPenalty(int i, SparseVector<double>* w) {
+    const double z = w->value(i);
+    double w_i = z;
+    double q_i = q_.value(i);
+    if (w_i > 0.0)
+      w_i = std::max(0.0, w_i - (u_ + q_i));
+    else if (w_i < 0.0)
+      w_i = std::min(0.0, w_i + (u_ - q_i));
+    q_i += w_i - z;
+    if (q_i == 0.0)
+      q_.erase(i);
+    else
+      q_.set_value(i, q_i);
+    if (w_i == 0.0)
+      w->erase(i);
+    else
+      w->set_value(i, w_i);
+  }
+
+  const double C_;  // reguarlization strength
+  double u_;
+  SparseVector<double> q_;
+};
+
+#endif
-- 
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