def save_sbml(filename, model, y0=None, volume=<NUM_LIT:1.0>, is_valid=True):
y0 = y0 or {}<EOL>import libsbml<EOL>document = export_sbml(model, y0, volume, is_valid)<EOL>libsbml.writeSBML(document, filename)<EOL>
Save a model in the SBML format.

Parameters
----------
model : NetworkModel
y0 : dict
    Initial condition.
volume : Real or Real3, optional
    A size of the simulation volume.
is_valid : bool, optional
    Check if the generated model is valid. True as a default.