Add MatSparse::submatrix.

src/faust_linear_operator/CPU/faust_MatSparse.h

@@ -352,6 +352,9 @@ namespace Faust
 
 			const FPP& operator()(faust_unsigned_int i, faust_unsigned_int j)const{return const_cast<Eigen::SparseMatrix<FPP,Eigen::RowMajor>*>(&mat)->coeffRef(i,j);}
 
+
+
+			void submatrix(const std::vector<int> &row_ids, const std::vector<int> &col_ids, MatDense<FPP, Cpu> & submat) const;
 			Vect<FPP,Cpu> get_col(faust_unsigned_int id) const;
 			void get_col(faust_unsigned_int id, Vect<FPP, Cpu> &out_vec) const;
 			/*

src/faust_linear_operator/CPU/faust_MatSparse.hpp

@@ -904,6 +904,16 @@ Real<FPP> Faust::MatSparse<FPP, Cpu>::normInf(faust_unsigned_int& row_id, const
 	return normL1(row_id, !transpose);
 }
 
+template<typename FPP>
+void Faust::MatSparse<FPP, Cpu>::submatrix(const std::vector<int> &row_ids, const std::vector<int> &col_ids, MatDense<FPP, Cpu> & submat) const
+{
+	if(this->dim1 != row_ids.size() || this->dim2 != col_ids.size())
+		submat.resize(row_ids.size(), col_ids.size());
+	for(int i=0;i<row_ids.size();i++)
+		for(int j=0;j<col_ids.size();j++)
+			submat.mat(i,j) = mat.coeff(row_ids[i], col_ids[j]);
+}
+
 template<typename FPP>
 Faust::Vect<FPP,Cpu> Faust::MatSparse<FPP,Cpu>::get_col(faust_unsigned_int id) const
 {