key-value mapping in C inside R?

Why not use a sparse Matrix package?
Hadley

In the original arima.c code the matrix is represented as an array of double.
I'd like to add a minimal overhead/changes on the code.

I think I'll use a simple sorted linked list to store the key-value map.
It will be enough for testing and I'll use something better if needed.

Thanks,
Matteo Bertini