Re: oct function question

[Søren Hauberg]

Hi,

Anand Patil skrev:
> OK: I'm writing lightweight oct functions that get called millions of 
> times that involve nonlinear operations on matrix elements. Past 
> experience with such situations in C++ indicates that the overhead from 
> any function calls or indirection involved in using Matrix's get and set 
> functions may add up. Is there any way to get the address of the 
> underlying array out of the Matrix class, as with the mex function 
> mxGetPr()?
Since newer versions of Octave support most of the mex interface, you 
can just use that. But you can also use "fortran_vec" function. But I'd 
recommend using the index operators,

  Matrix a(30, 30, 0); // Create a 30x30 matrix of zeros
  a(10, 10) = 7; // Remember to use zero-based indexes in C++


> Also: Is there any way to construct a Matrix so that it shares its 
> underlying array with another Matrix? That is, is it possible to pass a 
> matrix into an oct function but then work with it under a name other 
> than args(i).matrix_value()?
You can just use
  Matrix a = args(i).matrix_value();
and then work on a.

Søren