commented testCOMBoost

Framework/Utilities/testCOMBoost.cc

@@ -39,33 +39,42 @@ TEST_CASE("boosts") {
     return E * E / cSquared - p.squaredNorm();
   };
 
-  MassType const projectileMass = 4_GeV / cSquared;
-  Vector<momentum_d> pProjectileLab{rootCS, {0_GeV / c, 100_GeV / c, 0_GeV / c}};
+  // define projectile kinematics in lab frame
+  MassType const projectileMass = 1._GeV / cSquared;
+  Vector<momentum_d> pProjectileLab{rootCS, {0_GeV / c, 1_PeV / c, 0_GeV / c}};
   EnergyType const eProjectileLab = energy(projectileMass, pProjectileLab);
 
+  // define target kinematics in lab frame
   MassType const targetMass = 1_GeV / cSquared;
   Vector<momentum_d> pTargetLab{rootCS, {0_Ns, 0_Ns, 0_Ns}};
   EnergyType const eTargetLab = energy(targetMass, pTargetLab);
 
+  // define boost to com frame
   COMBoost boost(eProjectileLab, pProjectileLab, targetMass);
 
+  // boost projecticle
   auto const [eProjectileCoM, pProjectileCoM] =
       boost.toCoM(eProjectileLab, pProjectileLab);
+      
+  // boost target
   auto const [eTargetCoM, pTargetCoM] = boost.toCoM(eTargetLab, pTargetLab);
 
+  // sum of momenta in CoM, should be 0
   auto const sumPCoM = pProjectileCoM + pTargetCoM;
+  CHECK(sumPCoM[2] / (1_GeV / c) == Approx(0).margin(absMargin));
 
+  // mandelstam-s should be invariant under transformation
   CHECK(s(eProjectileLab + eTargetLab,
           pProjectileLab.GetComponents() + pTargetLab.GetComponents()) /
             (1_GeV / c) / (1_GeV / c) ==
         Approx(s(eProjectileCoM + eTargetCoM, pProjectileCoM + pTargetCoM) / (1_GeV / c) /
                (1_GeV / c)));
 
-  CHECK(sumPCoM[2] / (1_GeV / c) == Approx(0).margin(absMargin));
-
+  // boost back...
   auto const [eProjectileBack, pProjectileBack] =
       boost.fromCoM(eProjectileCoM, pProjectileCoM);
 
+  // ...should yield original values before the boosts
   CHECK(eProjectileBack / eProjectileLab == Approx(1));
   CHECK((pProjectileBack - pProjectileLab).norm() / (1_GeV / c) ==
         Approx(0).margin(absMargin));