fPsi functions for edges

I need to make a common module for mesh, many functions for elements are
shared.

Also, try to reduce the 'select type' statements, but I don't know
enough Fortran for it.

src/modules/mesh/moduleMeshBoundary.f90

@@ -223,12 +223,19 @@ MODULE moduleMeshBoundary
 
       class(meshEdge), intent(inout):: edge
       class(particle), intent(inout):: part
+      real(8), allocatable:: density(:)
+      integer:: nNodes
+      integer, allocatable:: nodes(:)
+
 
       select type(bound => edge%boundary%bTypes(part%species%n)%obj)
       type is(boundaryQuasiNeutrality)
+        nNodes = edge%nNodes
+        nodes  = edge%getNodes(nNodes)
+
         bound%alpha = 1.0d-1
 
-        if (random() < bound%alpha) then
+        if (random() <= bound%alpha) then
           call reflection(edge, part)
 
         else