Marked some static variables as const for clarity.

cc: @valsson

src/function/Matheval.cpp

@@ -29,7 +29,7 @@ using namespace std;
 namespace PLMD {
 namespace function {
 
-static std::map<string, double> leptonConstants= {
+const static std::map<string, double> leptonConstants= {
   {"e", std::exp(1.0)},
   {"log2e", 1.0/std::log(2.0)},
   {"log10e", 1.0/std::log(10.0)},

src/tools/SwitchingFunction.cpp

@@ -29,7 +29,7 @@
 using namespace std;
 namespace PLMD {
 
-static std::map<string, double> leptonConstants= {
+const static std::map<string, double> leptonConstants= {
   {"e", std::exp(1.0)},
   {"log2e", 1.0/std::log(2.0)},
   {"log10e", 1.0/std::log(10.0)},

src/tools/Tools.cpp

@@ -35,7 +35,7 @@
 using namespace std;
 namespace PLMD {
 
-static std::map<string, double> leptonConstants= {
+const static std::map<string, double> leptonConstants= {
   {"e", std::exp(1.0)},
   {"log2e", 1.0/std::log(2.0)},
   {"log10e", 1.0/std::log(10.0)},

src/ves/BF_Custom.cpp

@@ -29,7 +29,7 @@
 namespace PLMD {
 namespace ves {
 
-static std::map<std::string, double> leptonConstants= {
+const static std::map<std::string, double> leptonConstants= {
   {"e", std::exp(1.0)},
   {"log2e", 1.0/std::log(2.0)},
   {"log10e", 1.0/std::log(10.0)},

src/ves/TD_Custom.cpp

@@ -32,7 +32,7 @@
 namespace PLMD {
 namespace ves {
 
-static std::map<std::string, double> leptonConstants= {
+const static std::map<std::string, double> leptonConstants= {
   {"e", std::exp(1.0)},
   {"log2e", 1.0/std::log(2.0)},
   {"log10e", 1.0/std::log(10.0)},