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+/**
+ * @file gensvm_sparse.h
+ * @author Gertjan van den Burg
+ * @date 2016-10-11
+ * @brief Header file for gensvm_sparse.c
+ *
+ * @details
+ * Contains declarations of the GenSparse structure and related functions.
+ *
+ * @copyright
+
+ This program is free software; you can redistribute it and/or
+ modify it under the terms of the GNU General Public License
+ as published by the Free Software Foundation; either version 2
+ of the License, or (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+
+ */
+
+#ifndef GENSVM_SPARSE_H
+#define GENSVM_SPARSE_H
+
+// includes
+#include "gensvm_globals.h"
+
+// type declarations
+
+/**
+ * @brief A structure to represent a sparse matrix in CSR format
+ *
+ * @details
+ * This structure holds a sparse matrix in the classic CSR format. Refer to
+ * <a href="https://en.wikipedia.org/wiki/Sparse_matrix">Wikipedia</a> for 
+ * more details. The total storage requirement for this format is 
+ * 2*nnz+n_row+1, so it only makes sense to use this format if the number of 
+ * nonzeros is smaller than @f$(n(m - 1) - 1)/2@f$.
+ *
+ * @note
+ * We use @f$n@f$ for rows, and @f$m@f$ for columns, to conform to GenSVM 
+ * notation. This is in exact contrast with the Wikipedia page.
+ *
+ * @param nnz 		number of nonzero elements
+ * @param n_row 	rows of the matrix
+ * @param n_col 	columns of the matrix
+ * @param values 	nonzero values (length nnz)
+ * @param ia 		row indices (length n+1)
+ * @param ja 		column indices (length nnz)
+ */
+struct GenSparse {
+	long nnz;
+	///< number of nonzero elements
+	long n_row;
+	///< number of rows of the original matrix
+	long n_col;
+	///< number of columns of the original matrix
+
+	double *values;
+	///< actual nonzero values, should be of length nnz
+	int *ia;
+	///< cumulative row lengths, should be of length n+1
+	int *ja;
+	///< column indices, should be of length nnz
+};
+
+struct GenSparse *gensvm_init_sparse();
+void gensvm_free_sparse(struct GenSparse *sp);
+long gensvm_count_nnz(double *A, long rows, long cols);
+bool gensvm_could_sparse(double *A, long rows, long cols);
+struct GenSparse *gensvm_dense_to_sparse(double *A, long rows, long cols);
+double *gensvm_sparse_to_dense(struct GenSparse *A);
+
+#endif