Change order of operations to slightly improve accuracy

moose-core/biophysics/DifBuffer.cpp

@@ -454,14 +454,14 @@ void DifBuffer::vReinit( const Eref& e, ProcPtr p )
 
 void DifBuffer::vFluxFromIn(const Eref& e,double innerC, double innerThickness)
 {
-  double dif = 2 * D_ * innerArea_ / (thickness_ + innerThickness)/ volume_;
+  double dif = 2 * D_  / volume_* innerArea_ / (thickness_ + innerThickness);
   Af_ += dif * innerC;
   Bf_ += dif;
 }
 
 void DifBuffer::vFluxFromOut(const Eref& e,double outerC, double outerThickness)
 {
-  double dif = 2 * D_ * outerArea_ / (thickness_ + outerThickness) / volume_;
+  double dif = 2 * D_  / volume_* outerArea_ / (thickness_ + outerThickness);
   Af_ += dif * outerC;
   Bf_ += dif;
 }

moose-core/biophysics/DifShell.cpp

@@ -371,7 +371,7 @@ void DifShell::vBuffer(const Eref& e,
 
 void DifShell::vFluxFromOut(const Eref& e, double outerC, double outerThickness )
 {
-  double diff =2.*  D_  *  outerArea_ / (outerThickness + thickness_) /volume_;
+  double diff =2.*  D_ /volume_ *  outerArea_ / (outerThickness + thickness_) ;
   //influx from outer shell
   /**
    * We could pre-compute ( D / Volume ), but let us leave the optimizations
@@ -386,8 +386,7 @@ void DifShell::vFluxFromIn(const Eref& e, double innerC, double innerThickness )
 {
   //influx from inner shell
   //double dx = ( innerThickness + thickness_ ) / 2.0;
-  double diff = 2.* D_ * innerArea_ / (innerThickness + thickness_) /volume_;
-  //cout << "FluxFromIn "<<innerC<<" "<<innerThickness;
+  double diff = 2.* D_/volume_ * innerArea_ / (innerThickness + thickness_);
   dCbyDt_ +=  diff *  innerC ;
   Cmultiplier_ += diff ;
 }