slight change to eval_f s

Also added dependencies and instruction to README

README.md

@@ -7,6 +7,30 @@ This simulation of the Vlasov-Poisson system dimensions uses
 
 ______________________________________________________________________
 
+# How to use
+
+## Dependencies:
+
+- [deal.ii](https://dealii.org/) >= 9.6.0
+- OpenMP
+- [perf](https://perfwiki.github.io/main/) + [flameGraph](https://github.com/brendangregg/FlameGraph) (optional)
+
+After cloning the repo to your machine `cd` into it and run:
+
+```
+mkdir -p build; cd build/
+cmake ..
+make
+cd ..
+```
+
+Then check/change `parameters.lua` and run with `./build/nufi_poisson`.
+If you want to run with a [FlameGraph](https://www.brendangregg.com/flamegraphs.html) visualization at the end use `./run`.
+
+______________________________________________________________________
+
+# Further description
+
 dimensions: 1x1v
 
 status: builds, runs

src/nufi_solver.cc

@@ -32,6 +32,7 @@ std::vector<double> NuFISolver::eval_ftilda(
     const std::vector<SolutionSnapshot<1>> &phi_history) const {
 
   size_t x_size = X.size();
+  const double dt = Parameters::DT;
 
   std::vector<double> U(x_size, u);
   std::vector<double> results(x_size);
@@ -47,7 +48,7 @@ std::vector<double> NuFISolver::eval_ftilda(
   // We omit the initial half-step.
   while (--n) {
     for (size_t i = 0; i < x_size; ++i)
-      X[i] = X[i] - Parameters::DT * U[i];
+      X[i] = X[i] - dt * U[i];
 
     AssertThrow(
         phi_history[n].solution.size() ==
@@ -68,13 +69,13 @@ std::vector<double> NuFISolver::eval_ftilda(
 
     for (size_t i = 0; i < x_size; ++i) {
       Ex[i] = -tmp[i];
-      U[i] = U[i] + Parameters::DT * Ex[i];
+      U[i] = U[i] + dt * Ex[i];
     }
   }
 
   // The final half-step.
   for (size_t i = 0; i < x_size; ++i)
-    X[i] = X[i] - Parameters::DT * U[i];
+    X[i] = X[i] - dt * U[i];
 
   tmp = eval(X, grid_struct[phi_history[n].grid_version],
              phi_history[n].solution); // call eval only once
@@ -92,7 +93,7 @@ std::vector<double>
 NuFISolver::eval_f(unsigned int n, std::vector<double> X, double u,
                    const std::vector<GridStructure<1>> &grid_struct,
                    const std::vector<SolutionSnapshot<1>> &phi_history) const {
-
+  const double dt = Parameters::DT;
   size_t x_size = X.size();
 
   std::vector<double> U(x_size, u);
@@ -111,30 +112,30 @@ NuFISolver::eval_f(unsigned int n, std::vector<double> X, double u,
              phi_history[n].solution); // call eval only once
   for (size_t i = 0; i < x_size; ++i) {
     Ex[i] = -tmp[i];
-    U[i] = U[i] + 0.5 * Parameters::DT * Ex[i];
+    U[i] = U[i] + 0.5 * dt * Ex[i];
   }
 
   while (--n) {
     for (size_t i = 0; i < x_size; ++i)
-      X[i] = X[i] - Parameters::DT * U[i];
+      X[i] = X[i] - dt * U[i];
 
     tmp = eval(X, grid_struct[phi_history[n].grid_version],
                phi_history[n].solution); // call eval only once
     for (size_t i = 0; i < x_size; ++i) {
       Ex[i] = -tmp[i];
-      U[i] = U[i] + Parameters::DT * Ex[i];
+      U[i] = U[i] + dt * Ex[i];
     }
   }
 
   // The final half-step.
   for (size_t i = 0; i < x_size; ++i)
-    X[i] = X[i] - Parameters::DT * U[i];
+    X[i] = X[i] - dt * U[i];
 
   tmp = eval(X, grid_struct[phi_history[n].grid_version],
              phi_history[n].solution); // call eval only once
   for (size_t i = 0; i < x_size; ++i) {
     Ex[i] = -tmp[i];
-    U[i] = U[i] + 0.5 * Parameters::DT * Ex[i];
+    U[i] = U[i] + 0.5 * dt * Ex[i];
   }
 
   for (size_t i = 0; i < x_size; ++i)