Library function capabilities of Mathematica - wolfram-mathematica

Question

I am trying to use CUSP as an external linear solver for Mathematica to use the power of the GPU.
Here is the CUSP Project webpage. I am asking for some suggestion how we can integrate CUSP with Mathematica. I am sure many of you here will be interested to discuss this. I think writing a input matrix and then feeding it to CUSP program is not the way to go. Using Mathematica's LibrarayFunctionLoad will be a better way to pipeline the input matrix to the GPU based solver on the fly. What will be the way to supply the matrix and the right hand side matrix directly from Mathematica?
Here is some CUSP code snippet.
#include <cusp/hyb_matrix.h>
#include <cusp/io/matrix_market.h>
#include <cusp/krylov/cg.h>
int main(void)
{
// create an empty sparse matrix structure (HYB format)
cusp::hyb_matrix<int, float, cusp::device_memory> A;
// load a matrix stored in MatrixMarket format
cusp::io::read_matrix_market_file(A, "5pt_10x10.mtx");
// allocate storage for solution (x) and right hand side (b)
cusp::array1d<float, cusp::device_memory> x(A.num_rows, 0);
cusp::array1d<float, cusp::device_memory> b(A.num_rows, 1);
// solve the linear system A * x = b with the Conjugate Gradient method
cusp::krylov::cg(A, x, b);
return 0;
}
This question gives us the possibility to discuss compilation capabilities of Mathematica 8. It is also possible to invoke the topic of mathlink interface of MMA. I hope people here find this problem worthy and interesting enough to ponder on.
BR

Answer 1

If you want to use LibraryLink (for which LibraryFunctionLoad is used to access a dynamic library function as a Mathematica downvalue) there's actually not much room for discussion, LibraryFunctions can receive Mathematica tensors of machine doubles or machine integers and you're done.
The Mathematica MTensor format is a dense array, just as you'd naturally use in C, so if CUSP uses some other format you will need to write some glue code to translate between representations.
Refer to the LibraryLink tutorial for full details.
You will want to especially note the section "Memory Management of MTensors" in the Interaction with Mathematica page, and choose the "Shared" mode to just pass a Mathematica tensor by reference.