diff --git a/internal/ceres/sparse_matrix.h b/internal/ceres/sparse_matrix.h
new file mode 100644
index 0000000..074d847
--- /dev/null
+++ b/internal/ceres/sparse_matrix.h
@@ -0,0 +1,107 @@
+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2015 Google Inc. All rights reserved.
+// http://ceres-solver.org/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: sameeragarwal@google.com (Sameer Agarwal)
+//
+// Interface definition for sparse matrices.
+
+#ifndef CERES_INTERNAL_SPARSE_MATRIX_H_
+#define CERES_INTERNAL_SPARSE_MATRIX_H_
+
+#include <cstdio>
+#include "ceres/linear_operator.h"
+#include "ceres/internal/eigen.h"
+#include "ceres/types.h"
+
+namespace ceres {
+namespace internal {
+
+// This class defines the interface for storing and manipulating
+// sparse matrices. The key property that differentiates different
+// sparse matrices is how they are organized in memory and how the
+// information about the sparsity structure of the matrix is
+// stored. This has significant implications for linear solvers
+// operating on these matrices.
+//
+// To deal with the different kinds of layouts, we will assume that a
+// sparse matrix will have a two part representation. A values array
+// that will be used to store the entries of the sparse matrix and
+// some sort of a layout object that tells the user the sparsity
+// structure and layout of the values array. For example in case of
+// the TripletSparseMatrix, this information is carried in the rows
+// and cols arrays and for the BlockSparseMatrix, this information is
+// carried in the CompressedRowBlockStructure object.
+//
+// This interface deliberately does not contain any information about
+// the structure of the sparse matrix as that seems to be highly
+// matrix type dependent and we are at this stage unable to come up
+// with an efficient high level interface that spans multiple sparse
+// matrix types.
+class SparseMatrix : public LinearOperator {
+ public:
+  virtual ~SparseMatrix();
+
+  // y += Ax;
+  virtual void RightMultiply(const double* x, double* y) const = 0;
+  // y += A'x;
+  virtual void LeftMultiply(const double* x, double* y) const = 0;
+
+  // In MATLAB notation sum(A.*A, 1)
+  virtual void SquaredColumnNorm(double* x) const = 0;
+  // A = A * diag(scale)
+  virtual void ScaleColumns(const double* scale) = 0;
+
+  // A = 0. A->num_nonzeros() == 0 is true after this call. The
+  // sparsity pattern is preserved.
+  virtual void SetZero() = 0;
+
+  // Resize and populate dense_matrix with a dense version of the
+  // sparse matrix.
+  virtual void ToDenseMatrix(Matrix* dense_matrix) const = 0;
+
+  // Write out the matrix as a sequence of (i,j,s) triplets. This
+  // format is useful for loading the matrix into MATLAB/octave as a
+  // sparse matrix.
+  virtual void ToTextFile(FILE* file) const = 0;
+
+  // Accessors for the values array that stores the entries of the
+  // sparse matrix. The exact interpretation of the values of this
+  // array depends on the particular kind of SparseMatrix being
+  // accessed.
+  virtual double* mutable_values() = 0;
+  virtual const double* values() const = 0;
+
+  virtual int num_rows() const = 0;
+  virtual int num_cols() const = 0;
+  virtual int num_nonzeros() const = 0;
+};
+
+}  // namespace internal
+}  // namespace ceres
+
+#endif  // CERES_INTERNAL_SPARSE_MATRIX_H_