Developer's-corner/Boundary-Conditions.md

@@ -26,4 +26,36 @@ Adding a new boundary condition is a 2 step process, you need to:
 
 ### Implementing a stateless boundaries condition
 
-Then invoked, a stateless boundary condition does not remember anything from its previous invocation, 
+Then invoked, a stateless boundary condition does not remember anything from its previous invocations.
\ No newline at end of file
+
+One way of implementing such condition is to define a new function:
+
+```
+ using namespace fargOCA; // if necessary
+
+ void
+ SomeGreatBC(GasDisk& gas, real dt) {
+    do whatever need to be done to the gas object.
+ }
+```
+
+You can have a look to the already implemented conditions in [src/boundariesConditions.cpp](https://gitlab.oca.eu/DISC/fargOCA/blob/master/src/boundariesConditions.cpp): `ComputeReflectingZ`, `OpenBoundaryR` etc.
+
+### Declaring a stateless boundaries condition
+
+Let say you want to make your new condition available under the name "someGreatBC":
+
+In a carefully chosen source file ([src/boundariesConditions.cpp](https://gitlab.oca.eu/DISC/fargOCA/blob/master/src/boundariesConditions.cpp) for example):
+
+```
+...
+#include "boundariesConditions.hpp"
+...
+
+ using namespace fargOCA; // if necessary
+// Note: SomeGreatBC must be visible in scope
+
+  FctBoundariesHandler someGreatBc("someGreatBC", SomGreatBC);
+
+```
+You're done.