def METHOD_NAME(file_name):
    """ 
        Simple function that creates a new SBML model 'model1' with a non constant parameter x
    """
    doc = libsbml.SBMLDocument()
    model = doc.createModel()
    model.setId('model1')
    x = model.createParameter()
    x.setId('x')
    x.setValue(0)
    x.setConstant(False)
    libsbml.writeSBMLToFile(doc, file_name)