1.3.2.1 Solution clasnd-a

Question:

Classify the equations

$$u_{tt} - \nabla\cdot(p \nabla u) + q u = f \qquad - \nabla\cdot(p \nabla u) + q u = f$$

Answer:

Note for the second equation that there are no derivatives with respect to $t$ at all. Therefor, $t$ does not count as an independent variable for classification purposes. (It is a parameter in the solution.)