Problem with ldumatrix solver
 

Hello, friends, I'm now dealing with linear iterative solvers in Openfoam. After several days' code reading, I have got a small problem in ldumatrix solver.
I'm now reading the code of Preconditional CG method(PCG.C in Openfoam), and nearly have got through most of it. But there still exists a small problem in this part

// --- Calculate normalisation factor
scalar normFactor = this->normFactor(psi, source, wA, pA);

if (lduMatrix::debug >= 2)
{
Info<< " Normalisation factor = " << normFactor << endl;
}

// --- Calculate normalised residual norm
solverPerf.initialResidual() = gSumMag(rA)/normFactor;
solverPerf.finalResidual() = solverPerf.initialResidual();

I'm really curious with the normFactor part, which is defined in lduMatrixSolver.C

Foam::scalar Foam::lduMatrix::solver::normFactor
(
const scalarField& psi,
const scalarField& source,
const scalarField& Apsi,
scalarField& tmpField
) const
{
// --- Calculate A dot reference value of psi
matrix_.sumA(tmpField, interfaceBouCoeffs_, interfaces_);
tmpField *= gAverage(psi);

return
gSum(mag(Apsi - tmpField) + mag(source - tmpField))
+ solverPerformance::small_;

In this function, it seems to return |Ax-p|+|b-p|+Ɛ, which I can't find any relation with the definition of normalisation. In the comment, it says that the code wants to build up the normalised residual norm, but it should be rA/|rA|, so what does it mean in this part of code. Please help me figure out this problem.

Thank you for your time and regard
Frank Yu

Could anybody help me with this problem