clang-tidy fixes

Author: dpgrote

Source/Evolve/WarpXComputeDt.cpp

@@ -177,7 +177,7 @@ WarpX::DtLimitFromCyclotronFrequency ()
     const int n_containers = mypc->nContainers();
     for (int i = 0; i < n_containers; i++)
     {
-        WarpXParticleContainer& pc = mypc->GetParticleContainer(i);
+        const WarpXParticleContainer& pc = mypc->GetParticleContainer(i);
         if (pc.getMass() > 0.) {
             const amrex::Real pc_omegac = pc.getCharge()*B_max/pc.getMass();
             omegac_max = std::max(omegac_max, pc_omegac);

Source/Particles/MultiParticleContainer.cpp

@@ -696,7 +696,7 @@ MultiParticleContainer::GetChargeDensity (int lev, bool local)
 std::unique_ptr<amrex::MultiFab>
 MultiParticleContainer::GetGlobalPlasmaFrequency (int lev)
 {
-    WarpX & warpx = WarpX::GetInstance();
+    const WarpX & warpx = WarpX::GetInstance();
 
     amrex::BoxArray const & ba = warpx.boxArray(lev);
     amrex::DistributionMapping const & dmap = warpx.DistributionMap(lev);

Source/Particles/WarpXParticleContainer.cpp

@@ -2127,8 +2127,8 @@ WarpXParticleContainer::GetPlasmaFrequency (int lev)
     int const ng = 0;
     auto plasma_frequency = std::make_unique<amrex::MultiFab>(ba, dm, ncomps, ng);
 
-    amrex::Real const rmass = (amrex::Real)(m_mass);
-    amrex::Real const rcharge = (amrex::Real)(charge);
+    auto const rmass = (amrex::Real)(m_mass);
+    auto const rcharge = (amrex::Real)(charge);
     amrex::Real const Aconst = rcharge*rcharge/(rmass*PhysConst::epsilon_0);
 
 #ifdef AMREX_USE_OMP