[Toon-members] Efficient (dynamic) slicing

[Rafael Spring]

Hello gentlemen,

I'd like to learn a little bit about efficient dynamic slicing of  
Vectors and Matrices. Consider a situation where I hold a big Matrix  
in an object and want to fill that Matrix blockwise giving slices of  
the Matrix to an external function. Like this:

void fillSubMatrix(Matrix<>& slice) {
  // write something to the sclice...
}

class MyMainMatrix {
public:
  MyMainMatrix() : mMatrix(500, 10) {}

  void fillMatrix();

private:
  TooN::Matrix<> mMatrix;
};

void MyMainMatrix::fillMatrix() {
  int inc = 5;  // could be any number or dynamic

  for (unsigned int i = 0; i < mMatrix.num_rows(); i += inc) {
    fillSubMatrix(mMatrix.slice(i, 0, inc, mMatrix.num_cols()));
  }
}

Following thread http://lists.nongnu.org/archive/html/toon-members/ 
2007-06/msg00003.html there seem to be performance penalties using  
dynamic slicing. I assume the above code would also result in a  
temporary object (storage allocated from the heap) being constructed  
at each call to fillSubMatrix().
Would the following code be any better?

void fillSubMatrix(Matrix<-1, -1, double, TooN::Internal::Slice<-1,  
1> >& slice) {
  // write something to the sclice
}

Regards,
Rafael