LiveOilPvt: fix convergence criterium for oilSaturationPressure()

in some cases this pressure can be quite low (e.g. 0), and für
slightly inconsistent decks it can be even negative, so it makes sense
to compare the absolute values and to add an absolute convergence
criterion.

opm/material/fluidsystems/BlackOilFluidSystem.hpp

@@ -1,7 +1,7 @@
 // -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 // vi: set et ts=4 sw=4 sts=4:
 /*
-  Copyright (C) 2011-2013 by Andreas Lauser
+  Copyright (C) 2011-2015 by Andreas Lauser
 
   This file is part of the Open Porous Media project (OPM).
 
@@ -405,7 +405,6 @@ public:
         // calculate the mass fractions of gas and oil
         const auto& XoG = saturatedOilGasMassFraction(temperature, pressure, regionIdx);
 
-        // ATTENTION: XoG is represented by the _first_ axis!
         return oilFormationVolumeFactor(temperature, pressure, XoG, regionIdx);
     }
 

opm/material/fluidsystems/blackoilpvt/LiveOilPvt.hpp

@@ -482,7 +482,8 @@ private:
             const LhsEval& delta = f/fPrime;
             pSat -= delta;
 
-            if (std::abs(Toolbox::value(delta)) < Toolbox::value(pSat) * 1e-10)
+            Scalar absDelta = std::abs(Toolbox::value(delta));
+            if (absDelta < Toolbox::value(pSat) * 1e-10 || absDelta < 1e-4)
                 return pSat;
         }