def create_input(npart, domain=1.0):
    """Create input file for packing-generation program.

    Function creates ``generation.conf`` file with some default inputs.

    Args:
        npart (int): number of spheres
        domain (float, optional): size of domain
    """
    txt = (
        """Particles count: {0}
Packing size: {1} {1} {1}
Generation start: 1
Seed: 341
Steps to write: 1000
Boundaries mode: 1
Contraction rate: 1.328910e-005
    """
        .format(npart, domain))
    with open('generation.conf', 'w') as fout:
        fout.write(txt)
