Hi Jie Li,
I think something has happened to your original equation set. There is no separation between the variables, so the multiplications have been lost. For example, if you copy out the equations list and then do a Shift/Return, you get
{2 Dnena1 == a4Dse, Dsea4 == Dpe4a6 (-l + n + s),
a1n^2 + a2 == a4n + a5,
a7 + a6 (l - n - s)^2 ==
a5 + a4 (n + s), -a2nbE^bt - (a1enn^3 bE^bt)/3 ==
a + 2 Dnen (1 - E^bt), -a5bessE^bt -
1/2 a4esb E^bt (-n^2 + (n + s)^2) ==
0, -a7ep E^bt (l - n - s) + 1/3 epa6bE^bt (-l + n + s) == -a -
Dps4a6 (1 - E^bt) (-l + n + s)}
Eric
