[chris1980]

I want to do a volume average of volScalarField and from this scalar I want to calc the time devirative.

I have tried:

scalar dpmdt = ddt(p.weightedAverage(mesh.V()).value());

but the ddt function does not allow a scalar argument.

How can I do this?

[hjasak]

Basically, by hand: store several scalars and calculate the ddt directly from their values. A scalar variable is just a float (or a double) and it does not record its own history.

Hrv