Using faster switching functions in coordination and dhenergy

Coordination is now faster by approx 15% when using even
NN, even MM and d0=0

src/colvar/Coordination.cpp

@@ -106,7 +106,7 @@ CoordinationBase(ao)
 double Coordination::pairing(double distance,double&dfunc,unsigned i,unsigned j)const{
   (void) i; // avoid warnings
   (void) j; // avoid warnings
-  return switchingFunction.calculate(distance,dfunc);
+  return switchingFunction.calculateSqr(distance,dfunc);
 }
 
 }

src/colvar/CoordinationBase.cpp

@@ -156,7 +156,7 @@ void CoordinationBase::calculate()
   }
 
   double dfunc=0.;
-  ncoord += pairing(distance.modulo(), dfunc,i0,i1);
+  ncoord += pairing(distance.modulo2(), dfunc,i0,i1);
 
   deriv[i0] = deriv[i0] + (-dfunc)*distance ;
   deriv[i1] = deriv[i1] + dfunc*distance ;

src/colvar/DHEnergy.cpp

@@ -118,7 +118,8 @@ constant(0.0)
   log<<"  Bibliography "<<plumed.cite("Do, Carloni, Varani and Bussi, J. Chem. Theory Comput. 9, 1720 (2013)")<<" \n";
 }
 
-double DHEnergy::pairing(double distance,double&dfunc,unsigned i,unsigned j)const{
+double DHEnergy::pairing(double distance2,double&dfunc,unsigned i,unsigned j)const{
+  double distance=std::sqrt(distance2);
   if(getAbsoluteIndex(i)==getAbsoluteIndex(j)){
     dfunc=0.0;
     return 0.0;