The performance of the task is directly proportional to the number of bins in the energy grid (ie the number of rows of the matrix), while the scientific accuracy of the results of using the matrix improves (to the limit of the energy resolution of the instrument) the more rows there are in the matrix. This task by default uses the energy grid defined by the CAL to construct the response matrix. This grid currently contains approx 1000 bins for both PN and MOS instruments.
rmfgen now allows the user to specify his/her own grid, thereby allowing the user to decide at which point to compromise performance for accuracy. In addition, a user-specified grid will allow the user to restrict the matrix to a specific energy range of the instrument, and thus allow improved accuracy and a smaller RMF file as output, without having to sacrifice performance.
A user-defined grid can at present be only such that the grid points are evenly distributed across the energy range. It can be specified by setting withenergybins true and entering values for the parameters energymin, energymax and nenergybins.