1#!/usr/local/bin/python3.8 2r""" 3Speed of Sound 4============== 5 6This example shows how to compute the speed of sound by fitting phonon frequencies 7along selected directions by linear least-squares fit. 8For a command line interface use: 9 10 abiview.py ddb_vs input_DDB 11""" 12from __future__ import print_function 13 14import os 15import abipy.data as abidata 16 17from abipy import abilab 18from abipy.dfpt.vsound import SoundVelocity 19 20# Initialize object from DDB file. 21ddb_path = os.path.join(abidata.dirpath, "refs", "si_sound_vel", "Si_DDB") 22sv = SoundVelocity.from_ddb(ddb_path) 23 24# Get pandas dataframe with results. 25df = sv.get_dataframe() 26abilab.print_dataframe(df) 27 28# Plot fit 29sv.plot() 30