[cctbxbb] solvent mask

[celine Besnard]

Hi

I have a question about solvent mask in cctbx. I generated a mask using 
the mask manager. Then I am calculating the structure factors from the 
mask (using mask_manager.structure_factors() ). If I am trying to redo a 
map from the calculated structure factors (outside the cctbx and I hope 
without any scaling), I get a map with a mean density of zero, which is 
not the case of the original mask. I suppose that the 
structure_factors() function is doing some scaling at some point. In the 
source codes of the function structure_factors , I found

scale = miller_set.unit_cell().volume() / 
matrix.col(fft_manager.n_real()).product()
map_of_coeff *= scale

from_map = maptbx.structure_factors.from_map(
miller_set.space_group(),
anomalous_flag,
miller_set.indices(),
map_of_coeff,
conjugate_flag)

But I don't understand what the "scale line" is doing.

So I wonder what is exactly this 
matrix.col(fft_manager.n_real()).product() doing? And how do I generate 
structure factors for a mask without any scaling?

Thanks for any help

Celine