Mismatch between mathematical expressions and code implementation in PorousFlowDarcyBase::fullyUpwind function

[jltuhnu]

It seems there is a mismatch between the mathematical expressions on the web interface and the code implementation in the PorousFlowDarcyBase::fullyUpwind(JacRes res_or_jac, unsigned int ph, unsigned int pvar) function. Specifically, the following two lines:

_proto_flux[ph][n] *= mob;  
total_mass_out += _proto_flux[ph][n];  

as it does not align with the mathematical expressions described on the moose webpage https://mooseframework.inl.gov/modules/porous_flow/upwinding.html.

$$ I_{\mathrm{up}} = \sum_{I_{a}\geq 0}I_{a} \ \ \ \textrm{and}\ \ I_{\mathrm{down}} = -\sum_{I_{a}<0} I_{a} \ . $$

Then

$$ R_{a} = I_{a}\frac{I_{\mathrm{up}}}{I_{\mathrm{down}}} \ \ \ \textrm{for}\ \ \ I_{a}<0 \ . $$

and the code meaning:

$$ I_{\mathrm{up}} = \sum_{I_{a}\geq 0} m_{a} I_{a} \ \ \ \textrm{and}\ \ I_{\mathrm{down}} = -\sum_{I_{a}<0} I_{a} \ . $$