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+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// Copyright (C) 2008-2010 Gael Guennebaud <gael.guennebaud@inria.fr>
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef EIGEN_SPARSEMATRIX_H
+#define EIGEN_SPARSEMATRIX_H
+
+namespace Eigen { 
+
+/** \ingroup SparseCore_Module
+  *
+  * \class SparseMatrix
+  *
+  * \brief A versatible sparse matrix representation
+  *
+  * This class implements a more versatile variants of the common \em compressed row/column storage format.
+  * Each colmun's (resp. row) non zeros are stored as a pair of value with associated row (resp. colmiun) index.
+  * All the non zeros are stored in a single large buffer. Unlike the \em compressed format, there might be extra
+  * space inbetween the nonzeros of two successive colmuns (resp. rows) such that insertion of new non-zero
+  * can be done with limited memory reallocation and copies.
+  *
+  * A call to the function makeCompressed() turns the matrix into the standard \em compressed format
+  * compatible with many library.
+  *
+  * More details on this storage sceheme are given in the \ref TutorialSparse "manual pages".
+  *
+  * \tparam _Scalar the scalar type, i.e. the type of the coefficients
+  * \tparam _Options Union of bit flags controlling the storage scheme. Currently the only possibility
+  *                 is ColMajor or RowMajor. The default is 0 which means column-major.
+  * \tparam _Index the type of the indices. It has to be a \b signed type (e.g., short, int, std::ptrdiff_t). Default is \c int.
+  *
+  * This class can be extended with the help of the plugin mechanism described on the page
+  * \ref TopicCustomizingEigen by defining the preprocessor symbol \c EIGEN_SPARSEMATRIX_PLUGIN.
+  */
+
+namespace internal {
+template<typename _Scalar, int _Options, typename _Index>
+struct traits<SparseMatrix<_Scalar, _Options, _Index> >
+{
+  typedef _Scalar Scalar;
+  typedef _Index Index;
+  typedef Sparse StorageKind;
+  typedef MatrixXpr XprKind;
+  enum {
+    RowsAtCompileTime = Dynamic,
+    ColsAtCompileTime = Dynamic,
+    MaxRowsAtCompileTime = Dynamic,
+    MaxColsAtCompileTime = Dynamic,
+    Flags = _Options | NestByRefBit | LvalueBit,
+    CoeffReadCost = NumTraits<Scalar>::ReadCost,
+    SupportedAccessPatterns = InnerRandomAccessPattern
+  };
+};
+
+template<typename _Scalar, int _Options, typename _Index, int DiagIndex>
+struct traits<Diagonal<const SparseMatrix<_Scalar, _Options, _Index>, DiagIndex> >
+{
+  typedef SparseMatrix<_Scalar, _Options, _Index> MatrixType;
+  typedef typename nested<MatrixType>::type MatrixTypeNested;
+  typedef typename remove_reference<MatrixTypeNested>::type _MatrixTypeNested;
+
+  typedef _Scalar Scalar;
+  typedef Dense StorageKind;
+  typedef _Index Index;
+  typedef MatrixXpr XprKind;
+
+  enum {
+    RowsAtCompileTime = Dynamic,
+    ColsAtCompileTime = 1,
+    MaxRowsAtCompileTime = Dynamic,
+    MaxColsAtCompileTime = 1,
+    Flags = 0,
+    CoeffReadCost = _MatrixTypeNested::CoeffReadCost*10
+  };
+};
+
+} // end namespace internal
+
+template<typename _Scalar, int _Options, typename _Index>
+class SparseMatrix
+  : public SparseMatrixBase<SparseMatrix<_Scalar, _Options, _Index> >
+{
+  public:
+    EIGEN_SPARSE_PUBLIC_INTERFACE(SparseMatrix)
+    EIGEN_SPARSE_INHERIT_ASSIGNMENT_OPERATOR(SparseMatrix, +=)
+    EIGEN_SPARSE_INHERIT_ASSIGNMENT_OPERATOR(SparseMatrix, -=)
+
+    typedef MappedSparseMatrix<Scalar,Flags> Map;
+    using Base::IsRowMajor;
+    typedef internal::CompressedStorage<Scalar,Index> Storage;
+    enum {
+      Options = _Options
+    };
+
+  protected:
+
+    typedef SparseMatrix<Scalar,(Flags&~RowMajorBit)|(IsRowMajor?RowMajorBit:0)> TransposedSparseMatrix;
+
+    Index m_outerSize;
+    Index m_innerSize;
+    Index* m_outerIndex;
+    Index* m_innerNonZeros;     // optional, if null then the data is compressed
+    Storage m_data;
+    
+    Eigen::Map<Matrix<Index,Dynamic,1> > innerNonZeros() { return Eigen::Map<Matrix<Index,Dynamic,1> >(m_innerNonZeros, m_innerNonZeros?m_outerSize:0); }
+    const  Eigen::Map<const Matrix<Index,Dynamic,1> > innerNonZeros() const { return Eigen::Map<const Matrix<Index,Dynamic,1> >(m_innerNonZeros, m_innerNonZeros?m_outerSize:0); }
+
+  public:
+    
+    /** \returns whether \c *this is in compressed form. */
+    inline bool isCompressed() const { return m_innerNonZeros==0; }
+
+    /** \returns the number of rows of the matrix */
+    inline Index rows() const { return IsRowMajor ? m_outerSize : m_innerSize; }
+    /** \returns the number of columns of the matrix */
+    inline Index cols() const { return IsRowMajor ? m_innerSize : m_outerSize; }
+
+    /** \returns the number of rows (resp. columns) of the matrix if the storage order column major (resp. row major) */
+    inline Index innerSize() const { return m_innerSize; }
+    /** \returns the number of columns (resp. rows) of the matrix if the storage order column major (resp. row major) */
+    inline Index outerSize() const { return m_outerSize; }
+    
+    /** \returns a const pointer to the array of values.
+      * This function is aimed at interoperability with other libraries.
+      * \sa innerIndexPtr(), outerIndexPtr() */
+    inline const Scalar* valuePtr() const { return m_data.valuePtr(); }
+    /** \returns a non-const pointer to the array of values.
+      * This function is aimed at interoperability with other libraries.
+      * \sa innerIndexPtr(), outerIndexPtr() */
+    inline Scalar* valuePtr() { return m_data.valuePtr(); }
+
+    /** \returns a const pointer to the array of inner indices.
+      * This function is aimed at interoperability with other libraries.
+      * \sa valuePtr(), outerIndexPtr() */
+    inline const Index* innerIndexPtr() const { return m_data.indexPtr(); }
+    /** \returns a non-const pointer to the array of inner indices.
+      * This function is aimed at interoperability with other libraries.
+      * \sa valuePtr(), outerIndexPtr() */
+    inline Index* innerIndexPtr() { return m_data.indexPtr(); }
+
+    /** \returns a const pointer to the array of the starting positions of the inner vectors.
+      * This function is aimed at interoperability with other libraries.
+      * \sa valuePtr(), innerIndexPtr() */
+    inline const Index* outerIndexPtr() const { return m_outerIndex; }
+    /** \returns a non-const pointer to the array of the starting positions of the inner vectors.
+      * This function is aimed at interoperability with other libraries.
+      * \sa valuePtr(), innerIndexPtr() */
+    inline Index* outerIndexPtr() { return m_outerIndex; }
+
+    /** \returns a const pointer to the array of the number of non zeros of the inner vectors.
+      * This function is aimed at interoperability with other libraries.
+      * \warning it returns the null pointer 0 in compressed mode */
+    inline const Index* innerNonZeroPtr() const { return m_innerNonZeros; }
+    /** \returns a non-const pointer to the array of the number of non zeros of the inner vectors.
+      * This function is aimed at interoperability with other libraries.
+      * \warning it returns the null pointer 0 in compressed mode */
+    inline Index* innerNonZeroPtr() { return m_innerNonZeros; }
+
+    /** \internal */
+    inline Storage& data() { return m_data; }
+    /** \internal */
+    inline const Storage& data() const { return m_data; }
+
+    /** \returns the value of the matrix at position \a i, \a j
+      * This function returns Scalar(0) if the element is an explicit \em zero */
+    inline Scalar coeff(Index row, Index col) const
+    {
+      eigen_assert(row>=0 && row<rows() && col>=0 && col<cols());
+      
+      const Index outer = IsRowMajor ? row : col;
+      const Index inner = IsRowMajor ? col : row;
+      Index end = m_innerNonZeros ? m_outerIndex[outer] + m_innerNonZeros[outer] : m_outerIndex[outer+1];
+      return m_data.atInRange(m_outerIndex[outer], end, inner);
+    }
+
+    /** \returns a non-const reference to the value of the matrix at position \a i, \a j
+      *
+      * If the element does not exist then it is inserted via the insert(Index,Index) function
+      * which itself turns the matrix into a non compressed form if that was not the case.
+      *
+      * This is a O(log(nnz_j)) operation (binary search) plus the cost of insert(Index,Index)
+      * function if the element does not already exist.
+      */
+    inline Scalar& coeffRef(Index row, Index col)
+    {
+      eigen_assert(row>=0 && row<rows() && col>=0 && col<cols());
+      
+      const Index outer = IsRowMajor ? row : col;
+      const Index inner = IsRowMajor ? col : row;
+
+      Index start = m_outerIndex[outer];
+      Index end = m_innerNonZeros ? m_outerIndex[outer] + m_innerNonZeros[outer] : m_outerIndex[outer+1];
+      eigen_assert(end>=start && "you probably called coeffRef on a non finalized matrix");
+      if(end<=start)
+        return insert(row,col);
+      const Index p = m_data.searchLowerIndex(start,end-1,inner);
+      if((p<end) && (m_data.index(p)==inner))
+        return m_data.value(p);
+      else
+        return insert(row,col);
+    }
+
+    /** \returns a reference to a novel non zero coefficient with coordinates \a row x \a col.
+      * The non zero coefficient must \b not already exist.
+      *
+      * If the matrix \c *this is in compressed mode, then \c *this is turned into uncompressed
+      * mode while reserving room for 2 non zeros per inner vector. It is strongly recommended to first
+      * call reserve(const SizesType &) to reserve a more appropriate number of elements per
+      * inner vector that better match your scenario.
+      *
+      * This function performs a sorted insertion in O(1) if the elements of each inner vector are
+      * inserted in increasing inner index order, and in O(nnz_j) for a random insertion.
+      *
+      */
+    Scalar& insert(Index row, Index col)
+    {
+      eigen_assert(row>=0 && row<rows() && col>=0 && col<cols());
+      
+      if(isCompressed())
+      {
+        reserve(Matrix<Index,Dynamic,1>::Constant(outerSize(), 2));
+      }
+      return insertUncompressed(row,col);
+    }
+
+  public:
+
+    class InnerIterator;
+    class ReverseInnerIterator;
+
+    /** Removes all non zeros but keep allocated memory */
+    inline void setZero()
+    {
+      m_data.clear();
+      memset(m_outerIndex, 0, (m_outerSize+1)*sizeof(Index));
+      if(m_innerNonZeros)
+        memset(m_innerNonZeros, 0, (m_outerSize)*sizeof(Index));
+    }
+
+    /** \returns the number of non zero coefficients */
+    inline Index nonZeros() const
+    {
+      if(m_innerNonZeros)
+        return innerNonZeros().sum();
+      return static_cast<Index>(m_data.size());
+    }
+
+    /** Preallocates \a reserveSize non zeros.
+      *
+      * Precondition: the matrix must be in compressed mode. */
+    inline void reserve(Index reserveSize)
+    {
+      eigen_assert(isCompressed() && "This function does not make sense in non compressed mode.");
+      m_data.reserve(reserveSize);
+    }
+    
+    #ifdef EIGEN_PARSED_BY_DOXYGEN
+    /** Preallocates \a reserveSize[\c j] non zeros for each column (resp. row) \c j.
+      *
+      * This function turns the matrix in non-compressed mode */
+    template<class SizesType>
+    inline void reserve(const SizesType& reserveSizes);
+    #else
+    template<class SizesType>
+    inline void reserve(const SizesType& reserveSizes, const typename SizesType::value_type& enableif = typename SizesType::value_type())
+    {
+      EIGEN_UNUSED_VARIABLE(enableif);
+      reserveInnerVectors(reserveSizes);
+    }
+    template<class SizesType>
+    inline void reserve(const SizesType& reserveSizes, const typename SizesType::Scalar& enableif =
+    #if (!defined(_MSC_VER)) || (_MSC_VER>=1500) // MSVC 2005 fails to compile with this typename
+        typename
+    #endif
+        SizesType::Scalar())
+    {
+      EIGEN_UNUSED_VARIABLE(enableif);
+      reserveInnerVectors(reserveSizes);
+    }
+    #endif // EIGEN_PARSED_BY_DOXYGEN
+  protected:
+    template<class SizesType>
+    inline void reserveInnerVectors(const SizesType& reserveSizes)
+    {
+      if(isCompressed())
+      {
+        std::size_t totalReserveSize = 0;
+        // turn the matrix into non-compressed mode
+        m_innerNonZeros = static_cast<Index*>(std::malloc(m_outerSize * sizeof(Index)));
+        if (!m_innerNonZeros) internal::throw_std_bad_alloc();
+        
+        // temporarily use m_innerSizes to hold the new starting points.
+        Index* newOuterIndex = m_innerNonZeros;
+        
+        Index count = 0;
+        for(Index j=0; j<m_outerSize; ++j)
+        {
+          newOuterIndex[j] = count;
+          count += reserveSizes[j] + (m_outerIndex[j+1]-m_outerIndex[j]);
+          totalReserveSize += reserveSizes[j];
+        }
+        m_data.reserve(totalReserveSize);
+        Index previousOuterIndex = m_outerIndex[m_outerSize];
+        for(Index j=m_outerSize-1; j>=0; --j)
+        {
+          Index innerNNZ = previousOuterIndex - m_outerIndex[j];
+          for(Index i=innerNNZ-1; i>=0; --i)
+          {
+            m_data.index(newOuterIndex[j]+i) = m_data.index(m_outerIndex[j]+i);
+            m_data.value(newOuterIndex[j]+i) = m_data.value(m_outerIndex[j]+i);
+          }
+          previousOuterIndex = m_outerIndex[j];
+          m_outerIndex[j] = newOuterIndex[j];
+          m_innerNonZeros[j] = innerNNZ;
+        }
+        m_outerIndex[m_outerSize] = m_outerIndex[m_outerSize-1] + m_innerNonZeros[m_outerSize-1] + reserveSizes[m_outerSize-1];
+        
+        m_data.resize(m_outerIndex[m_outerSize]);
+      }
+      else
+      {
+        Index* newOuterIndex = static_cast<Index*>(std::malloc((m_outerSize+1)*sizeof(Index)));
+        if (!newOuterIndex) internal::throw_std_bad_alloc();
+        
+        Index count = 0;
+        for(Index j=0; j<m_outerSize; ++j)
+        {
+          newOuterIndex[j] = count;
+          Index alreadyReserved = (m_outerIndex[j+1]-m_outerIndex[j]) - m_innerNonZeros[j];
+          Index toReserve = std::max<Index>(reserveSizes[j], alreadyReserved);
+          count += toReserve + m_innerNonZeros[j];
+        }
+        newOuterIndex[m_outerSize] = count;
+        
+        m_data.resize(count);
+        for(Index j=m_outerSize-1; j>=0; --j)
+        {
+          Index offset = newOuterIndex[j] - m_outerIndex[j];
+          if(offset>0)
+          {
+            Index innerNNZ = m_innerNonZeros[j];
+            for(Index i=innerNNZ-1; i>=0; --i)
+            {
+              m_data.index(newOuterIndex[j]+i) = m_data.index(m_outerIndex[j]+i);
+              m_data.value(newOuterIndex[j]+i) = m_data.value(m_outerIndex[j]+i);
+            }
+          }
+        }
+        
+        std::swap(m_outerIndex, newOuterIndex);
+        std::free(newOuterIndex);
+      }
+      
+    }
+  public:
+
+    //--- low level purely coherent filling ---
+
+    /** \internal
+      * \returns a reference to the non zero coefficient at position \a row, \a col assuming that:
+      * - the nonzero does not already exist
+      * - the new coefficient is the last one according to the storage order
+      *
+      * Before filling a given inner vector you must call the statVec(Index) function.
+      *
+      * After an insertion session, you should call the finalize() function.
+      *
+      * \sa insert, insertBackByOuterInner, startVec */
+    inline Scalar& insertBack(Index row, Index col)
+    {
+      return insertBackByOuterInner(IsRowMajor?row:col, IsRowMajor?col:row);
+    }
+
+    /** \internal
+      * \sa insertBack, startVec */
+    inline Scalar& insertBackByOuterInner(Index outer, Index inner)
+    {
+      eigen_assert(size_t(m_outerIndex[outer+1]) == m_data.size() && "Invalid ordered insertion (invalid outer index)");
+      eigen_assert( (m_outerIndex[outer+1]-m_outerIndex[outer]==0 || m_data.index(m_data.size()-1)<inner) && "Invalid ordered insertion (invalid inner index)");
+      Index p = m_outerIndex[outer+1];
+      ++m_outerIndex[outer+1];
+      m_data.append(0, inner);
+      return m_data.value(p);
+    }
+
+    /** \internal
+      * \warning use it only if you know what you are doing */
+    inline Scalar& insertBackByOuterInnerUnordered(Index outer, Index inner)
+    {
+      Index p = m_outerIndex[outer+1];
+      ++m_outerIndex[outer+1];
+      m_data.append(0, inner);
+      return m_data.value(p);
+    }
+
+    /** \internal
+      * \sa insertBack, insertBackByOuterInner */
+    inline void startVec(Index outer)
+    {
+      eigen_assert(m_outerIndex[outer]==Index(m_data.size()) && "You must call startVec for each inner vector sequentially");
+      eigen_assert(m_outerIndex[outer+1]==0 && "You must call startVec for each inner vector sequentially");
+      m_outerIndex[outer+1] = m_outerIndex[outer];
+    }
+
+    /** \internal
+      * Must be called after inserting a set of non zero entries using the low level compressed API.
+      */
+    inline void finalize()
+    {
+      if(isCompressed())
+      {
+        Index size = static_cast<Index>(m_data.size());
+        Index i = m_outerSize;
+        // find the last filled column
+        while (i>=0 && m_outerIndex[i]==0)
+          --i;
+        ++i;
+        while (i<=m_outerSize)
+        {
+          m_outerIndex[i] = size;
+          ++i;
+        }
+      }
+    }
+
+    //---
+
+    template<typename InputIterators>
+    void setFromTriplets(const InputIterators& begin, const InputIterators& end);
+
+    void sumupDuplicates();
+
+    //---
+    
+    /** \internal
+      * same as insert(Index,Index) except that the indices are given relative to the storage order */
+    Scalar& insertByOuterInner(Index j, Index i)
+    {
+      return insert(IsRowMajor ? j : i, IsRowMajor ? i : j);
+    }
+
+    /** Turns the matrix into the \em compressed format.
+      */
+    void makeCompressed()
+    {
+      if(isCompressed())
+        return;
+      
+      Index oldStart = m_outerIndex[1];
+      m_outerIndex[1] = m_innerNonZeros[0];
+      for(Index j=1; j<m_outerSize; ++j)
+      {
+        Index nextOldStart = m_outerIndex[j+1];
+        Index offset = oldStart - m_outerIndex[j];
+        if(offset>0)
+        {
+          for(Index k=0; k<m_innerNonZeros[j]; ++k)
+          {
+            m_data.index(m_outerIndex[j]+k) = m_data.index(oldStart+k);
+            m_data.value(m_outerIndex[j]+k) = m_data.value(oldStart+k);
+          }
+        }
+        m_outerIndex[j+1] = m_outerIndex[j] + m_innerNonZeros[j];
+        oldStart = nextOldStart;
+      }
+      std::free(m_innerNonZeros);
+      m_innerNonZeros = 0;
+      m_data.resize(m_outerIndex[m_outerSize]);
+      m_data.squeeze();
+    }
+
+    /** Turns the matrix into the uncompressed mode */
+    void uncompress()
+    {
+      if(m_innerNonZeros != 0)
+        return; 
+      m_innerNonZeros = static_cast<Index*>(std::malloc(m_outerSize * sizeof(Index)));
+      for (Index i = 0; i < m_outerSize; i++)
+      {
+        m_innerNonZeros[i] = m_outerIndex[i+1] - m_outerIndex[i]; 
+      }
+    }
+    
+    /** Suppresses all nonzeros which are \b much \b smaller \b than \a reference under the tolerence \a epsilon */
+    void prune(const Scalar& reference, const RealScalar& epsilon = NumTraits<RealScalar>::dummy_precision())
+    {
+      prune(default_prunning_func(reference,epsilon));
+    }
+    
+    /** Turns the matrix into compressed format, and suppresses all nonzeros which do not satisfy the predicate \a keep.
+      * The functor type \a KeepFunc must implement the following function:
+      * \code
+      * bool operator() (const Index& row, const Index& col, const Scalar& value) const;
+      * \endcode
+      * \sa prune(Scalar,RealScalar)
+      */
+    template<typename KeepFunc>
+    void prune(const KeepFunc& keep = KeepFunc())
+    {
+      // TODO optimize the uncompressed mode to avoid moving and allocating the data twice
+      // TODO also implement a unit test
+      makeCompressed();
+
+      Index k = 0;
+      for(Index j=0; j<m_outerSize; ++j)
+      {
+        Index previousStart = m_outerIndex[j];
+        m_outerIndex[j] = k;
+        Index end = m_outerIndex[j+1];
+        for(Index i=previousStart; i<end; ++i)
+        {
+          if(keep(IsRowMajor?j:m_data.index(i), IsRowMajor?m_data.index(i):j, m_data.value(i)))
+          {
+            m_data.value(k) = m_data.value(i);
+            m_data.index(k) = m_data.index(i);
+            ++k;
+          }
+        }
+      }
+      m_outerIndex[m_outerSize] = k;
+      m_data.resize(k,0);
+    }
+
+    /** Resizes the matrix to a \a rows x \a cols matrix leaving old values untouched.
+      * \sa resizeNonZeros(Index), reserve(), setZero()
+      */
+    void conservativeResize(Index rows, Index cols) 
+    {
+      // No change
+      if (this->rows() == rows && this->cols() == cols) return;
+      
+      // If one dimension is null, then there is nothing to be preserved
+      if(rows==0 || cols==0) return resize(rows,cols);
+
+      Index innerChange = IsRowMajor ? cols - this->cols() : rows - this->rows();
+      Index outerChange = IsRowMajor ? rows - this->rows() : cols - this->cols();
+      Index newInnerSize = IsRowMajor ? cols : rows;
+
+      // Deals with inner non zeros
+      if (m_innerNonZeros)
+      {
+        // Resize m_innerNonZeros
+        Index *newInnerNonZeros = static_cast<Index*>(std::realloc(m_innerNonZeros, (m_outerSize + outerChange) * sizeof(Index)));
+        if (!newInnerNonZeros) internal::throw_std_bad_alloc();
+        m_innerNonZeros = newInnerNonZeros;
+        
+        for(Index i=m_outerSize; i<m_outerSize+outerChange; i++)          
+          m_innerNonZeros[i] = 0;
+      } 
+      else if (innerChange < 0) 
+      {
+        // Inner size decreased: allocate a new m_innerNonZeros
+        m_innerNonZeros = static_cast<Index*>(std::malloc((m_outerSize+outerChange+1) * sizeof(Index)));
+        if (!m_innerNonZeros) internal::throw_std_bad_alloc();
+        for(Index i = 0; i < m_outerSize; i++)
+          m_innerNonZeros[i] = m_outerIndex[i+1] - m_outerIndex[i];
+      }
+      
+      // Change the m_innerNonZeros in case of a decrease of inner size
+      if (m_innerNonZeros && innerChange < 0)
+      {
+        for(Index i = 0; i < m_outerSize + (std::min)(outerChange, Index(0)); i++)
+        {
+          Index &n = m_innerNonZeros[i];
+          Index start = m_outerIndex[i];
+          while (n > 0 && m_data.index(start+n-1) >= newInnerSize) --n; 
+        }
+      }
+      
+      m_innerSize = newInnerSize;
+
+      // Re-allocate outer index structure if necessary
+      if (outerChange == 0)
+        return;
+          
+      Index *newOuterIndex = static_cast<Index*>(std::realloc(m_outerIndex, (m_outerSize + outerChange + 1) * sizeof(Index)));
+      if (!newOuterIndex) internal::throw_std_bad_alloc();
+      m_outerIndex = newOuterIndex;
+      if (outerChange > 0)
+      {
+        Index last = m_outerSize == 0 ? 0 : m_outerIndex[m_outerSize];
+        for(Index i=m_outerSize; i<m_outerSize+outerChange+1; i++)          
+          m_outerIndex[i] = last; 
+      }
+      m_outerSize += outerChange;
+    }
+    
+    /** Resizes the matrix to a \a rows x \a cols matrix and initializes it to zero.
+      * \sa resizeNonZeros(Index), reserve(), setZero()
+      */
+    void resize(Index rows, Index cols)
+    {
+      const Index outerSize = IsRowMajor ? rows : cols;
+      m_innerSize = IsRowMajor ? cols : rows;
+      m_data.clear();
+      if (m_outerSize != outerSize || m_outerSize==0)
+      {
+        std::free(m_outerIndex);
+        m_outerIndex = static_cast<Index*>(std::malloc((outerSize + 1) * sizeof(Index)));
+        if (!m_outerIndex) internal::throw_std_bad_alloc();
+        
+        m_outerSize = outerSize;
+      }
+      if(m_innerNonZeros)
+      {
+        std::free(m_innerNonZeros);
+        m_innerNonZeros = 0;
+      }
+      memset(m_outerIndex, 0, (m_outerSize+1)*sizeof(Index));
+    }
+
+    /** \internal
+      * Resize the nonzero vector to \a size */
+    void resizeNonZeros(Index size)
+    {
+      // TODO remove this function
+      m_data.resize(size);
+    }
+
+    /** \returns a const expression of the diagonal coefficients */
+    const Diagonal<const SparseMatrix> diagonal() const { return *this; }
+
+    /** Default constructor yielding an empty \c 0 \c x \c 0 matrix */
+    inline SparseMatrix()
+      : m_outerSize(-1), m_innerSize(0), m_outerIndex(0), m_innerNonZeros(0)
+    {
+      check_template_parameters();
+      resize(0, 0);
+    }
+
+    /** Constructs a \a rows \c x \a cols empty matrix */
+    inline SparseMatrix(Index rows, Index cols)
+      : m_outerSize(0), m_innerSize(0), m_outerIndex(0), m_innerNonZeros(0)
+    {
+      check_template_parameters();
+      resize(rows, cols);
+    }
+
+    /** Constructs a sparse matrix from the sparse expression \a other */
+    template<typename OtherDerived>
+    inline SparseMatrix(const SparseMatrixBase<OtherDerived>& other)
+      : m_outerSize(0), m_innerSize(0), m_outerIndex(0), m_innerNonZeros(0)
+    {
+      EIGEN_STATIC_ASSERT((internal::is_same<Scalar, typename OtherDerived::Scalar>::value),
+        YOU_MIXED_DIFFERENT_NUMERIC_TYPES__YOU_NEED_TO_USE_THE_CAST_METHOD_OF_MATRIXBASE_TO_CAST_NUMERIC_TYPES_EXPLICITLY)
+      check_template_parameters();
+      *this = other.derived();
+    }
+    
+    /** Constructs a sparse matrix from the sparse selfadjoint view \a other */
+    template<typename OtherDerived, unsigned int UpLo>
+    inline SparseMatrix(const SparseSelfAdjointView<OtherDerived, UpLo>& other)
+      : m_outerSize(0), m_innerSize(0), m_outerIndex(0), m_innerNonZeros(0)
+    {
+      check_template_parameters();
+      *this = other;
+    }
+
+    /** Copy constructor (it performs a deep copy) */
+    inline SparseMatrix(const SparseMatrix& other)
+      : Base(), m_outerSize(0), m_innerSize(0), m_outerIndex(0), m_innerNonZeros(0)
+    {
+      check_template_parameters();
+      *this = other.derived();
+    }
+
+    /** \brief Copy constructor with in-place evaluation */
+    template<typename OtherDerived>
+    SparseMatrix(const ReturnByValue<OtherDerived>& other)
+      : Base(), m_outerSize(0), m_innerSize(0), m_outerIndex(0), m_innerNonZeros(0)
+    {
+      check_template_parameters();
+      initAssignment(other);
+      other.evalTo(*this);
+    }
+
+    /** Swaps the content of two sparse matrices of the same type.
+      * This is a fast operation that simply swaps the underlying pointers and parameters. */
+    inline void swap(SparseMatrix& other)
+    {
+      //EIGEN_DBG_SPARSE(std::cout << "SparseMatrix:: swap\n");
+      std::swap(m_outerIndex, other.m_outerIndex);
+      std::swap(m_innerSize, other.m_innerSize);
+      std::swap(m_outerSize, other.m_outerSize);
+      std::swap(m_innerNonZeros, other.m_innerNonZeros);
+      m_data.swap(other.m_data);
+    }
+
+    /** Sets *this to the identity matrix.
+      * This function also turns the matrix into compressed mode, and drop any reserved memory. */
+    inline void setIdentity()
+    {
+      eigen_assert(rows() == cols() && "ONLY FOR SQUARED MATRICES");
+      this->m_data.resize(rows());
+      Eigen::Map<Matrix<Index, Dynamic, 1> >(this->m_data.indexPtr(), rows()).setLinSpaced(0, rows()-1);
+      Eigen::Map<Matrix<Scalar, Dynamic, 1> >(this->m_data.valuePtr(), rows()).setOnes();
+      Eigen::Map<Matrix<Index, Dynamic, 1> >(this->m_outerIndex, rows()+1).setLinSpaced(0, rows());
+      std::free(m_innerNonZeros);
+      m_innerNonZeros = 0;
+    }
+    inline SparseMatrix& operator=(const SparseMatrix& other)
+    {
+      if (other.isRValue())
+      {
+        swap(other.const_cast_derived());
+      }
+      else if(this!=&other)
+      {
+        initAssignment(other);
+        if(other.isCompressed())
+        {
+          memcpy(m_outerIndex, other.m_outerIndex, (m_outerSize+1)*sizeof(Index));
+          m_data = other.m_data;
+        }
+        else
+        {
+          Base::operator=(other);
+        }
+      }
+      return *this;
+    }
+
+    #ifndef EIGEN_PARSED_BY_DOXYGEN
+    template<typename Lhs, typename Rhs>
+    inline SparseMatrix& operator=(const SparseSparseProduct<Lhs,Rhs>& product)
+    { return Base::operator=(product); }
+    
+    template<typename OtherDerived>
+    inline SparseMatrix& operator=(const ReturnByValue<OtherDerived>& other)
+    {
+      initAssignment(other);
+      return Base::operator=(other.derived());
+    }
+    
+    template<typename OtherDerived>
+    inline SparseMatrix& operator=(const EigenBase<OtherDerived>& other)
+    { return Base::operator=(other.derived()); }
+    #endif
+
+    template<typename OtherDerived>
+    EIGEN_DONT_INLINE SparseMatrix& operator=(const SparseMatrixBase<OtherDerived>& other);
+
+    friend std::ostream & operator << (std::ostream & s, const SparseMatrix& m)
+    {
+      EIGEN_DBG_SPARSE(
+        s << "Nonzero entries:\n";
+        if(m.isCompressed())
+          for (Index i=0; i<m.nonZeros(); ++i)
+            s << "(" << m.m_data.value(i) << "," << m.m_data.index(i) << ") ";
+        else
+          for (Index i=0; i<m.outerSize(); ++i)
+          {
+            Index p = m.m_outerIndex[i];
+            Index pe = m.m_outerIndex[i]+m.m_innerNonZeros[i];
+            Index k=p;
+            for (; k<pe; ++k)
+              s << "(" << m.m_data.value(k) << "," << m.m_data.index(k) << ") ";
+            for (; k<m.m_outerIndex[i+1]; ++k)
+              s << "(_,_) ";
+          }
+        s << std::endl;
+        s << std::endl;
+        s << "Outer pointers:\n";
+        for (Index i=0; i<m.outerSize(); ++i)
+          s << m.m_outerIndex[i] << " ";
+        s << " $" << std::endl;
+        if(!m.isCompressed())
+        {
+          s << "Inner non zeros:\n";
+          for (Index i=0; i<m.outerSize(); ++i)
+            s << m.m_innerNonZeros[i] << " ";
+          s << " $" << std::endl;
+        }
+        s << std::endl;
+      );
+      s << static_cast<const SparseMatrixBase<SparseMatrix>&>(m);
+      return s;
+    }
+
+    /** Destructor */
+    inline ~SparseMatrix()
+    {
+      std::free(m_outerIndex);
+      std::free(m_innerNonZeros);
+    }
+
+#ifndef EIGEN_PARSED_BY_DOXYGEN
+    /** Overloaded for performance */
+    Scalar sum() const;
+#endif
+    
+#   ifdef EIGEN_SPARSEMATRIX_PLUGIN
+#     include EIGEN_SPARSEMATRIX_PLUGIN
+#   endif
+
+protected:
+
+    template<typename Other>
+    void initAssignment(const Other& other)
+    {
+      resize(other.rows(), other.cols());
+      if(m_innerNonZeros)
+      {
+        std::free(m_innerNonZeros);
+        m_innerNonZeros = 0;
+      }
+    }
+
+    /** \internal
+      * \sa insert(Index,Index) */
+    EIGEN_DONT_INLINE Scalar& insertCompressed(Index row, Index col);
+
+    /** \internal
+      * A vector object that is equal to 0 everywhere but v at the position i */
+    class SingletonVector
+    {
+        Index m_index;
+        Index m_value;
+      public:
+        typedef Index value_type;
+        SingletonVector(Index i, Index v)
+          : m_index(i), m_value(v)
+        {}
+
+        Index operator[](Index i) const { return i==m_index ? m_value : 0; }
+    };
+
+    /** \internal
+      * \sa insert(Index,Index) */
+    EIGEN_DONT_INLINE Scalar& insertUncompressed(Index row, Index col);
+
+public:
+    /** \internal
+      * \sa insert(Index,Index) */
+    EIGEN_STRONG_INLINE Scalar& insertBackUncompressed(Index row, Index col)
+    {
+      const Index outer = IsRowMajor ? row : col;
+      const Index inner = IsRowMajor ? col : row;
+
+      eigen_assert(!isCompressed());
+      eigen_assert(m_innerNonZeros[outer]<=(m_outerIndex[outer+1] - m_outerIndex[outer]));
+
+      Index p = m_outerIndex[outer] + m_innerNonZeros[outer]++;
+      m_data.index(p) = inner;
+      return (m_data.value(p) = 0);
+    }
+
+private:
+  static void check_template_parameters()
+  {
+    EIGEN_STATIC_ASSERT(NumTraits<Index>::IsSigned,THE_INDEX_TYPE_MUST_BE_A_SIGNED_TYPE);
+    EIGEN_STATIC_ASSERT((Options&(ColMajor|RowMajor))==Options,INVALID_MATRIX_TEMPLATE_PARAMETERS);
+  }
+
+  struct default_prunning_func {
+    default_prunning_func(const Scalar& ref, const RealScalar& eps) : reference(ref), epsilon(eps) {}
+    inline bool operator() (const Index&, const Index&, const Scalar& value) const
+    {
+      return !internal::isMuchSmallerThan(value, reference, epsilon);
+    }
+    Scalar reference;
+    RealScalar epsilon;
+  };
+};
+
+template<typename Scalar, int _Options, typename _Index>
+class SparseMatrix<Scalar,_Options,_Index>::InnerIterator
+{
+  public:
+    InnerIterator(const SparseMatrix& mat, Index outer)
+      : m_values(mat.valuePtr()), m_indices(mat.innerIndexPtr()), m_outer(outer), m_id(mat.m_outerIndex[outer])
+    {
+      if(mat.isCompressed())
+        m_end = mat.m_outerIndex[outer+1];
+      else
+        m_end = m_id + mat.m_innerNonZeros[outer];
+    }
+
+    inline InnerIterator& operator++() { m_id++; return *this; }
+
+    inline const Scalar& value() const { return m_values[m_id]; }
+    inline Scalar& valueRef() { return const_cast<Scalar&>(m_values[m_id]); }
+
+    inline Index index() const { return m_indices[m_id]; }
+    inline Index outer() const { return m_outer; }
+    inline Index row() const { return IsRowMajor ? m_outer : index(); }
+    inline Index col() const { return IsRowMajor ? index() : m_outer; }
+
+    inline operator bool() const { return (m_id < m_end); }
+
+  protected:
+    const Scalar* m_values;
+    const Index* m_indices;
+    const Index m_outer;
+    Index m_id;
+    Index m_end;
+};
+
+template<typename Scalar, int _Options, typename _Index>
+class SparseMatrix<Scalar,_Options,_Index>::ReverseInnerIterator
+{
+  public:
+    ReverseInnerIterator(const SparseMatrix& mat, Index outer)
+      : m_values(mat.valuePtr()), m_indices(mat.innerIndexPtr()), m_outer(outer), m_start(mat.m_outerIndex[outer])
+    {
+      if(mat.isCompressed())
+        m_id = mat.m_outerIndex[outer+1];
+      else
+        m_id = m_start + mat.m_innerNonZeros[outer];
+    }
+
+    inline ReverseInnerIterator& operator--() { --m_id; return *this; }
+
+    inline const Scalar& value() const { return m_values[m_id-1]; }
+    inline Scalar& valueRef() { return const_cast<Scalar&>(m_values[m_id-1]); }
+
+    inline Index index() const { return m_indices[m_id-1]; }
+    inline Index outer() const { return m_outer; }
+    inline Index row() const { return IsRowMajor ? m_outer : index(); }
+    inline Index col() const { return IsRowMajor ? index() : m_outer; }
+
+    inline operator bool() const { return (m_id > m_start); }
+
+  protected:
+    const Scalar* m_values;
+    const Index* m_indices;
+    const Index m_outer;
+    Index m_id;
+    const Index m_start;
+};
+
+namespace internal {
+
+template<typename InputIterator, typename SparseMatrixType>
+void set_from_triplets(const InputIterator& begin, const InputIterator& end, SparseMatrixType& mat, int Options = 0)
+{
+  EIGEN_UNUSED_VARIABLE(Options);
+  enum { IsRowMajor = SparseMatrixType::IsRowMajor };
+  typedef typename SparseMatrixType::Scalar Scalar;
+  typedef typename SparseMatrixType::Index Index;
+  SparseMatrix<Scalar,IsRowMajor?ColMajor:RowMajor,Index> trMat(mat.rows(),mat.cols());
+
+  if(begin!=end)
+  {
+    // pass 1: count the nnz per inner-vector
+    Matrix<Index,Dynamic,1> wi(trMat.outerSize());
+    wi.setZero();
+    for(InputIterator it(begin); it!=end; ++it)
+    {
+      eigen_assert(it->row()>=0 && it->row()<mat.rows() && it->col()>=0 && it->col()<mat.cols());
+      wi(IsRowMajor ? it->col() : it->row())++;
+    }
+
+    // pass 2: insert all the elements into trMat
+    trMat.reserve(wi);
+    for(InputIterator it(begin); it!=end; ++it)
+      trMat.insertBackUncompressed(it->row(),it->col()) = it->value();
+
+    // pass 3:
+    trMat.sumupDuplicates();
+  }
+
+  // pass 4: transposed copy -> implicit sorting
+  mat = trMat;
+}
+
+}
+
+
+/** Fill the matrix \c *this with the list of \em triplets defined by the iterator range \a begin - \a end.
+  *
+  * A \em triplet is a tuple (i,j,value) defining a non-zero element.
+  * The input list of triplets does not have to be sorted, and can contains duplicated elements.
+  * In any case, the result is a \b sorted and \b compressed sparse matrix where the duplicates have been summed up.
+  * This is a \em O(n) operation, with \em n the number of triplet elements.
+  * The initial contents of \c *this is destroyed.
+  * The matrix \c *this must be properly resized beforehand using the SparseMatrix(Index,Index) constructor,
+  * or the resize(Index,Index) method. The sizes are not extracted from the triplet list.
+  *
+  * The \a InputIterators value_type must provide the following interface:
+  * \code
+  * Scalar value() const; // the value
+  * Scalar row() const;   // the row index i
+  * Scalar col() const;   // the column index j
+  * \endcode
+  * See for instance the Eigen::Triplet template class.
+  *
+  * Here is a typical usage example:
+  * \code
+    typedef Triplet<double> T;
+    std::vector<T> tripletList;
+    triplets.reserve(estimation_of_entries);
+    for(...)
+    {
+      // ...
+      tripletList.push_back(T(i,j,v_ij));
+    }
+    SparseMatrixType m(rows,cols);
+    m.setFromTriplets(tripletList.begin(), tripletList.end());
+    // m is ready to go!
+  * \endcode
+  *
+  * \warning The list of triplets is read multiple times (at least twice). Therefore, it is not recommended to define
+  * an abstract iterator over a complex data-structure that would be expensive to evaluate. The triplets should rather
+  * be explicitely stored into a std::vector for instance.
+  */
+template<typename Scalar, int _Options, typename _Index>
+template<typename InputIterators>
+void SparseMatrix<Scalar,_Options,_Index>::setFromTriplets(const InputIterators& begin, const InputIterators& end)
+{
+  internal::set_from_triplets(begin, end, *this);
+}
+
+/** \internal */
+template<typename Scalar, int _Options, typename _Index>
+void SparseMatrix<Scalar,_Options,_Index>::sumupDuplicates()
+{
+  eigen_assert(!isCompressed());
+  // TODO, in practice we should be able to use m_innerNonZeros for that task
+  Matrix<Index,Dynamic,1> wi(innerSize());
+  wi.fill(-1);
+  Index count = 0;
+  // for each inner-vector, wi[inner_index] will hold the position of first element into the index/value buffers
+  for(Index j=0; j<outerSize(); ++j)
+  {
+    Index start   = count;
+    Index oldEnd  = m_outerIndex[j]+m_innerNonZeros[j];
+    for(Index k=m_outerIndex[j]; k<oldEnd; ++k)
+    {
+      Index i = m_data.index(k);
+      if(wi(i)>=start)
+      {
+        // we already meet this entry => accumulate it
+        m_data.value(wi(i)) += m_data.value(k);
+      }
+      else
+      {
+        m_data.value(count) = m_data.value(k);
+        m_data.index(count) = m_data.index(k);
+        wi(i) = count;
+        ++count;
+      }
+    }
+    m_outerIndex[j] = start;
+  }
+  m_outerIndex[m_outerSize] = count;
+
+  // turn the matrix into compressed form
+  std::free(m_innerNonZeros);
+  m_innerNonZeros = 0;
+  m_data.resize(m_outerIndex[m_outerSize]);
+}
+
+template<typename Scalar, int _Options, typename _Index>
+template<typename OtherDerived>
+EIGEN_DONT_INLINE SparseMatrix<Scalar,_Options,_Index>& SparseMatrix<Scalar,_Options,_Index>::operator=(const SparseMatrixBase<OtherDerived>& other)
+{
+  EIGEN_STATIC_ASSERT((internal::is_same<Scalar, typename OtherDerived::Scalar>::value),
+        YOU_MIXED_DIFFERENT_NUMERIC_TYPES__YOU_NEED_TO_USE_THE_CAST_METHOD_OF_MATRIXBASE_TO_CAST_NUMERIC_TYPES_EXPLICITLY)
+  
+  const bool needToTranspose = (Flags & RowMajorBit) != (OtherDerived::Flags & RowMajorBit);
+  if (needToTranspose)
+  {
+    // two passes algorithm:
+    //  1 - compute the number of coeffs per dest inner vector
+    //  2 - do the actual copy/eval
+    // Since each coeff of the rhs has to be evaluated twice, let's evaluate it if needed
+    typedef typename internal::nested<OtherDerived,2>::type OtherCopy;
+    typedef typename internal::remove_all<OtherCopy>::type _OtherCopy;
+    OtherCopy otherCopy(other.derived());
+
+    SparseMatrix dest(other.rows(),other.cols());
+    Eigen::Map<Matrix<Index, Dynamic, 1> > (dest.m_outerIndex,dest.outerSize()).setZero();
+
+    // pass 1
+    // FIXME the above copy could be merged with that pass
+    for (Index j=0; j<otherCopy.outerSize(); ++j)
+      for (typename _OtherCopy::InnerIterator it(otherCopy, j); it; ++it)
+        ++dest.m_outerIndex[it.index()];
+
+    // prefix sum
+    Index count = 0;
+    Matrix<Index,Dynamic,1> positions(dest.outerSize());
+    for (Index j=0; j<dest.outerSize(); ++j)
+    {
+      Index tmp = dest.m_outerIndex[j];
+      dest.m_outerIndex[j] = count;
+      positions[j] = count;
+      count += tmp;
+    }
+    dest.m_outerIndex[dest.outerSize()] = count;
+    // alloc
+    dest.m_data.resize(count);
+    // pass 2
+    for (Index j=0; j<otherCopy.outerSize(); ++j)
+    {
+      for (typename _OtherCopy::InnerIterator it(otherCopy, j); it; ++it)
+      {
+        Index pos = positions[it.index()]++;
+        dest.m_data.index(pos) = j;
+        dest.m_data.value(pos) = it.value();
+      }
+    }
+    this->swap(dest);
+    return *this;
+  }
+  else
+  {
+    if(other.isRValue())
+      initAssignment(other.derived());
+    // there is no special optimization
+    return Base::operator=(other.derived());
+  }
+}
+
+template<typename _Scalar, int _Options, typename _Index>
+EIGEN_DONT_INLINE typename SparseMatrix<_Scalar,_Options,_Index>::Scalar& SparseMatrix<_Scalar,_Options,_Index>::insertUncompressed(Index row, Index col)
+{
+  eigen_assert(!isCompressed());
+
+  const Index outer = IsRowMajor ? row : col;
+  const Index inner = IsRowMajor ? col : row;
+
+  Index room = m_outerIndex[outer+1] - m_outerIndex[outer];
+  Index innerNNZ = m_innerNonZeros[outer];
+  if(innerNNZ>=room)
+  {
+    // this inner vector is full, we need to reallocate the whole buffer :(
+    reserve(SingletonVector(outer,std::max<Index>(2,innerNNZ)));
+  }
+
+  Index startId = m_outerIndex[outer];
+  Index p = startId + m_innerNonZeros[outer];
+  while ( (p > startId) && (m_data.index(p-1) > inner) )
+  {
+    m_data.index(p) = m_data.index(p-1);
+    m_data.value(p) = m_data.value(p-1);
+    --p;
+  }
+  eigen_assert((p<=startId || m_data.index(p-1)!=inner) && "you cannot insert an element that already exist, you must call coeffRef to this end");
+
+  m_innerNonZeros[outer]++;
+
+  m_data.index(p) = inner;
+  return (m_data.value(p) = 0);
+}
+
+template<typename _Scalar, int _Options, typename _Index>
+EIGEN_DONT_INLINE typename SparseMatrix<_Scalar,_Options,_Index>::Scalar& SparseMatrix<_Scalar,_Options,_Index>::insertCompressed(Index row, Index col)
+{
+  eigen_assert(isCompressed());
+
+  const Index outer = IsRowMajor ? row : col;
+  const Index inner = IsRowMajor ? col : row;
+
+  Index previousOuter = outer;
+  if (m_outerIndex[outer+1]==0)
+  {
+    // we start a new inner vector
+    while (previousOuter>=0 && m_outerIndex[previousOuter]==0)
+    {
+      m_outerIndex[previousOuter] = static_cast<Index>(m_data.size());
+      --previousOuter;
+    }
+    m_outerIndex[outer+1] = m_outerIndex[outer];
+  }
+
+  // here we have to handle the tricky case where the outerIndex array
+  // starts with: [ 0 0 0 0 0 1 ...] and we are inserted in, e.g.,
+  // the 2nd inner vector...
+  bool isLastVec = (!(previousOuter==-1 && m_data.size()!=0))
+                && (size_t(m_outerIndex[outer+1]) == m_data.size());
+
+  size_t startId = m_outerIndex[outer];
+  // FIXME let's make sure sizeof(long int) == sizeof(size_t)
+  size_t p = m_outerIndex[outer+1];
+  ++m_outerIndex[outer+1];
+
+  double reallocRatio = 1;
+  if (m_data.allocatedSize()<=m_data.size())
+  {
+    // if there is no preallocated memory, let's reserve a minimum of 32 elements
+    if (m_data.size()==0)
+    {
+      m_data.reserve(32);
+    }
+    else
+    {
+      // we need to reallocate the data, to reduce multiple reallocations
+      // we use a smart resize algorithm based on the current filling ratio
+      // in addition, we use double to avoid integers overflows
+      double nnzEstimate = double(m_outerIndex[outer])*double(m_outerSize)/double(outer+1);
+      reallocRatio = (nnzEstimate-double(m_data.size()))/double(m_data.size());
+      // furthermore we bound the realloc ratio to:
+      //   1) reduce multiple minor realloc when the matrix is almost filled
+      //   2) avoid to allocate too much memory when the matrix is almost empty
+      reallocRatio = (std::min)((std::max)(reallocRatio,1.5),8.);
+    }
+  }
+  m_data.resize(m_data.size()+1,reallocRatio);
+
+  if (!isLastVec)
+  {
+    if (previousOuter==-1)
+    {
+      // oops wrong guess.
+      // let's correct the outer offsets
+      for (Index k=0; k<=(outer+1); ++k)
+        m_outerIndex[k] = 0;
+      Index k=outer+1;
+      while(m_outerIndex[k]==0)
+        m_outerIndex[k++] = 1;
+      while (k<=m_outerSize && m_outerIndex[k]!=0)
+        m_outerIndex[k++]++;
+      p = 0;
+      --k;
+      k = m_outerIndex[k]-1;
+      while (k>0)
+      {
+        m_data.index(k) = m_data.index(k-1);
+        m_data.value(k) = m_data.value(k-1);
+        k--;
+      }
+    }
+    else
+    {
+      // we are not inserting into the last inner vec
+      // update outer indices:
+      Index j = outer+2;
+      while (j<=m_outerSize && m_outerIndex[j]!=0)
+        m_outerIndex[j++]++;
+      --j;
+      // shift data of last vecs:
+      Index k = m_outerIndex[j]-1;
+      while (k>=Index(p))
+      {
+        m_data.index(k) = m_data.index(k-1);
+        m_data.value(k) = m_data.value(k-1);
+        k--;
+      }
+    }
+  }
+
+  while ( (p > startId) && (m_data.index(p-1) > inner) )
+  {
+    m_data.index(p) = m_data.index(p-1);
+    m_data.value(p) = m_data.value(p-1);
+    --p;
+  }
+
+  m_data.index(p) = inner;
+  return (m_data.value(p) = 0);
+}
+
+} // end namespace Eigen
+
+#endif // EIGEN_SPARSEMATRIX_H