Question about data organization and writing

Hello,

my application iterates over a signal and, within each iteration, produces the following data to be stored into one single HDF5 file immediately:

- a matrix of floats with a known number of rows but unknown number of columns (different for each iteration),
- an integer, and
- a float

The number of iterations is not known a priori. The file should be usable within GNU Octave.

What HDF5 datatype(s) should be used and how should writing be carried out in each iteration?

Thank you.
Alex