This example tests the use of ph.x to calculate a part of the dynamical matrix. 

The calculation proceeds as follows:

1) make a self-consistent calculation for CH4 at the Gamma point
   (input=ch4.scf.in, output=ch4.scf.out).

2) make a phonon calculation at the Gamma point and calculate all the modes
   just for comparison.
   (input=ch4.phG.in, output=ch4.phG.out).

3) make a phonon calculation at the Gamma point and calculate only the mode
   with A1 symmetry.
   (input=ch4.phA1.in, output=ch4.phA1.out).

4) make a phonon calculation at the Gamma point and calculate only the
   modes with E symmetry. 
   (input=ch4.phE.in1, output=ch4.phE.out1).

5) recover previous calculation and finish the E mode.
   (input=ch4.phE.in2, output=ch4.phE.out2).