[parsing] Averaged perceptron model data structure for storing the finalized, averaged, sparse weights

src/averaged_perceptron.h

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+/*
+averaged_perceptron.h
+---------------------
+
+The averaged perceptron is a simple, efficient and effective method for
+training sequence models.
+
+The averaged perceptron is a linear model, meaning the score for a given class
+is the dot product of weights and the feature values.
+
+This implementation of the averaged perceptron uses a trie data structure to
+store the mapping from features to ids, which can be quite memory efficient
+as opposed to a hash table and allows us to store 
+
+The weights are stored as a sparse matrix in compressed sparse row format
+(see sparse_matrix.h)
+
+See [Collins, 2002] Discriminative Training Methods for Hidden Markov Models: 
+                    Theory and Experiments with Perceptron Algorithms
+
+Paper: http://www.cs.columbia.edu/~mcollins/papers/tagperc.pdf
+*/
+#ifndef AVERAGED_PERCEPTRON_H
+#define AVERAGED_PERCEPTRON_H
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+#include "collections.h"
+#include "sparse_matrix.h"
+#include "trie.h"
+
+typedef struct averaged_perceptron {
+    uint32_t num_features;
+    uint32_t num_classes;
+    trie_t *features;
+    cstring_array *classes;
+    sparse_matrix_t *weights;
+    double_array *scores;
+} averaged_perceptron_t;
+
+averaged_perceptron_t *averaged_perceptron_read(FILE *f);
+averaged_perceptron_t *averaged_perceptron_load(char *filename);
+
+uint32_t averaged_perceptron_predict(averaged_perceptron_t *self, cstring_array *features);
+uint32_t averaged_perceptron_predict_counts(averaged_perceptron_t *self, khash_t(str_uint32) *feature_counts);
+
+double_array *averaged_perceptron_predict_scores(averaged_perceptron_t *self, cstring_array *features);
+double_array *averaged_perceptron_predict_scores_counts(averaged_perceptron_t *self, khash_t(str_uint32) *feature_counts);
+
+bool averaged_perceptron_write(averaged_perceptron_t *self, FILE *f);
+bool averaged_perceptron_save(averaged_perceptron_t *self, char *filename);
+
+averaged_perceptron_t *averaged_perceptron_read(FILE *f);
+averaged_perceptron_t *averaged_perceptron_load(char *filename);
+
+void averaged_perceptron_destroy(averaged_perceptron_t *self);
+
+
+#endif