Remove incorrect statements about initial conditions (#601)

docs/src/manual/boundary_conditions.md

@@ -272,17 +272,4 @@ u = zeros(ndofs(dh))
 apply_analytical!(u, dh, :p, x -> ρ * g * x[2])
 ```
 
-See also [Time Dependent Problems](@ref) for one example. 
-
-*Note about solving DAE:* 
-A Differential Algebraic Equations (DAE) is an equation of the form
-``\boldsymbol{r}(\boldsymbol{u}(t),\boldsymbol{u}'(t),t)=\boldsymbol{0}``,
-which usually cannot be expressed as a true ODE. They occur often,
-but not always, in forms where some time derivatives are missing
-```math
-u_1'(t) = f(\boldsymbol{u}(t),t)
-0 = g(\boldsymbol{u}(t),t)`
-```
-In for such equations, it is usually necessary to specify initial conditions 
-for both ``\boldsymbol{u}(0)`` and ``\boldsymbol{u}'(0)``, and these must be consistent,
-i.e. ``\boldsymbol{r}(\boldsymbol{u}(0),\boldsymbol{u}'(0),0)=\boldsymbol{0}``.
+See also [Time Dependent Problems](@ref) for one example.