Modified THcAerogel::ReadDatabase

1) Need to add fNelem to DBRequest to read parameter arrays.
2) Added optional variable and set to true. Flag in the
DBRequest to tell code that parameter is optional
and does not have to be found.
3) Move setting of fNelem to before DBRequest for aero_num_pairs
 so that it can be overwritten by parameter file.

src/THcAerogel.cxx

@@ -112,11 +112,12 @@ Int_t THcAerogel::ReadDatabase( const TDatime& date )
   prefix[0]=tolower(GetApparatus()->GetName()[0]);
   prefix[1]='\0';
 
+  fNelem = 8;			// Default if not defined
+  Bool_t optional=true ;
   DBRequest listextra[]={
-    {"aero_num_pairs", &fNelem, kInt},
+    {"aero_num_pairs", &fNelem, kInt,0,optional},
     {0}
   };
-  fNelem = 8;			// Default if not defined
   gHcParms->LoadParmValues((DBRequest*)&listextra,prefix);
 
   fA_Pos = new Float_t[fNelem];
@@ -134,12 +135,12 @@ Int_t THcAerogel::ReadDatabase( const TDatime& date )
   fNegPedMean = new Double_t[fNelem];
 
   DBRequest list[]={
-    {"aero_pos_gain", fPosGain, kDouble},
-    {"aero_neg_gain", fPosGain, kDouble},
-    {"aero_pos_ped_limit", fPosPedLimit, kInt},
-    {"aero_neg_ped_limit", fNegPedLimit, kInt},
-    //    {"aero_pos_ped_mean", fPosPedMean, kDouble},
-    //    {"aero_neg_ped_mean", fNegPedMean, kDouble},
+    {"aero_pos_gain", fPosGain, kDouble, fNelem},
+    {"aero_neg_gain", fNegGain, kDouble, fNelem},
+    {"aero_pos_ped_limit", fPosPedLimit, kInt, fNelem},
+    {"aero_neg_ped_limit", fNegPedLimit, kInt, fNelem},
+    {"aero_pos_ped_mean", fPosPedMean, kDouble, fNelem,optional},
+    {"aero_neg_ped_mean", fNegPedMean, kDouble, fNelem,optional},
     {0}
   };
   gHcParms->LoadParmValues((DBRequest*)&list,prefix);