  Kumar et al. (2006) obtained a fifth order polynomial in $\omega$ for the
dispersion relation and pointed out that the calculations preformed by Porter
et al. (1994) and by Dwivedi & Pandey (2003) seem to be in error, as they
obtained a sixth order polynomial. The energy equation of Dwivedi & Pandey
(2003) was dimensionally wrong. Dwivedi & Pandey (2006) corrected the energy
equation and still claimed that the dispersion relation must be a sixth order
polynomial. The equations (11) $-$ (19) of Dwivedi & Pandey (2006) and the
equations (24) $-$ (32) Kumar et al. (2006) are the same. This fact has been
expressed by Kumar et al. (2006) themselves. Even then they tried to show this
set of equations on one side gives the sixth order polynomial as they got; on
the other side, the same set of equations gives the fifth order polynomial as
Kumar et al. (2006) obtained. The situation appears to be non-scientific, as
the system of equations is a linear one. These are simple algebraic equations
where the variables are to be eliminated. However, it is a matter of surprise
that by solving these equations, two scientific groups are getting polynomials
of different degrees. In the present discussion, we have attempted to short out
this discrepancy.
