Probleme de redéfinition d'operateur << et +

Bonjour,
j'ai un probleme pour redefinir l'operateur << et +

voici le code

#include <iostream>
#include <string>
#include <vector>

#include <stdlib.h>
#include <math.h>

//#include "/home/superpc/Documents/prog/cpp/osdefine.h"
//#include std_IO_h

using namespace std;

class Row
{
private :
vector<double> columns;
public :
Row()
{
}

Row(int size)
{
for(int i =0;i<size;i++)
{
columns.insert(columns.end(),0.0);
}
}

Row(const Row& aCopy)
{
vector<double> :: const_iterator iter;
for(iter=aCopy.columns.begin();iter!= aCopy.columns.end();iter++)
{
double d = (*iter);
columns.insert(columns.end(),d);
}
}

int size()
{
return columns.size();
}

double& operator[] (int index)
{
if(index<0|| index > columns.size())
{
throw "class Row : errAcess : indice du taleau hors limite";
}
return columns[index];
}
};

class Matrix
{
private :
vector<Row> rows;
public :
Matrix(int lign, int cols)
{
for(int i=0;i<lign;i++)
{
Row r(cols);
rows.insert(rows.end(),r);
}
}

Row& operator[] (int index)
{
if(index<0|| index > rows.size())
{
throw "class Matrix : errAcess : indice du taleau hors limite";
}
return rows[index];
}

std::ostream &operator << (Matrix& m);

int RowCount()
{
return rows.size();
}

int ColumnCount()
{
if(rows.size())
{
return rows[0].size();
}
return 0;
}

const Matrix operator+ (const Matrix m1,const Matrix m2)
{
if(m1.RowCount() != m2.RowCount())
{
throw "class Matrix : errSize : nombre de lignes invalide";
}

if(m1.ColumnCount() != m2.ColumnCount())
{
throw "class Matrix : errSize : nombre de colonnes invalide";
}

Matrix m(m1.RowCount(),m1.ColumnCount());

for(int r=0;r<m1.size();r++)
{
for(int(c=0;c<m1[r].size();c++)
{
m[r][c]=m1[r][c]+m2[r][c];
}
}

return m;
}
};

std::ostream & Matrix::operator << (Matrix &m)
{
std::ostream s <<"";

for(int r=0;r<rows.size();r++)
{
for(int c=0;c<rows[r].size();c++)
{
s<<m[r][c] << " ";
}
s << endl;
}
return s;
}