fix: readme and static const DT

advection/README.md

@@ -1,3 +1,28 @@
+## What is new?
+There is one new added component: `AdvectionKernel`s which is an "interface" (i.e an abstract class).
+There are two implementations simple Euler integration called `EulerIntegrationKernel` and 
+Runge Kutta integration called `RK4AdvectionKernel`.
+
+Main function gives a good example of how to use the library. Especially the following function which prints the
+position of the particle at every time step.
+```Cpp
+template <typename AdvectionKernelImpl>
+void advectForSomeTime(const UVGrid &uvGrid, const AdvectionKernelImpl &kernel, double latstart, double lonstart) {
+
+    // Require at compile time that kernel derives from the abstract class AdvectionKernel
+    static_assert(std::is_base_of<AdvectionKernel, AdvectionKernelImpl>::value, NotAKernelError);
+
+    double lat1 = latstart, lon1 = lonstart;
+    for(int time = 100; time <= 10000; time += AdvectionKernel::DT) {
+        cout << "lat = " << lat1 << " lon = " << lon1 << endl;
+        auto [templat, templon] = kernel.advect(time, lat1, lon1);
+        lat1 = templat;
+        lon1 = templon;
+    }
+}
+```
+
+
 ## Location of data
 The data path is hardcoded such that the following tree structure is assumed:
 ```

advection/src/AdvectionKernel.h

@@ -5,22 +5,23 @@
 
 #include "Vel.h"
 
-#define DT 50
 
 /*
  * Implement this class for every integration method.
  */
 class AdvectionKernel {
 public:
+    const static int DT = 50;
     /**
      * This function must take a time, latitude and longitude of a particle and must output
-     * a new latitude and longitude after being advected once for DT time as defined above.
+     * a new latitude and longitude after being advected once for AdvectionKernel::DT time as defined above.
      * @param time Time since the beginning of the data
      * @param latitude Latitude of particle
      * @param longitude Longitude of particle
      * @return A pair of latitude and longitude of particle.
      */
     virtual std::pair<double, double> advect(int time, double latitude, double longitude) const = 0;
+
 };
 
 #endif //ADVECTION_ADVECTIONKERNEL_H

advection/src/main.cpp

@@ -16,7 +16,7 @@ void advectForSomeTime(const UVGrid &uvGrid, const AdvectionKernelImpl &kernel,
     static_assert(std::is_base_of<AdvectionKernel, AdvectionKernelImpl>::value, NotAKernelError);
 
     double lat1 = latstart, lon1 = lonstart;
-    for(int time = 100; time <= 10000; time += DT) {
+    for(int time = 100; time <= 10000; time += AdvectionKernel::DT) {
         cout << "lat = " << lat1 << " lon = " << lon1 << endl;
         auto [templat, templon] = kernel.advect(time, lat1, lon1);
         lat1 = templat;