Fixed bug with number of collisions not computing correctly because

INT/REAL conversions.

Number of collisions now take into account the different weight of
particles inside a cell without impacting performance.

src/modules/moduleCollisions.f95

@@ -135,6 +135,7 @@ MODULE moduleCollisions
       vRel = species(1)%obj%m*NORM2(part_i%v - part_j%v)**2
       sigmaVrel = self%crossSec%get(vRel)*vRel
       sigmaVrelMaxNew = sigmaVrelMaxNew + sigmaVrel
+      PRINT *, sigmaVrelMaxNew/sigmaVrelMax, RAND()
       IF (sigmaVrelMaxNew/sigmaVrelMax > RAND()) THEN
         !Applies the collision
         v_i = NORM2(part_i%v)

src/modules/moduleMesh.f95

@@ -95,6 +95,8 @@ MODULE moduleMesh
     INTEGER(KIND=OMP_LOCK_KIND):: lock
     !Number of collisions per volume
     INTEGER:: nColl = 0
+    !Total weight of particles inside cell
+    REAL(8):: totalWeight = 0.D0
     CONTAINS
       PROCEDURE(initVol_interface),     DEFERRED, PASS:: init
       PROCEDURE(scatter_interface),     DEFERRED, PASS:: scatter

src/modules/moduleMeshCyl.f95

@@ -454,6 +454,7 @@ MODULE moduleMeshCyl
         !Assign particle to listPart_in
         CALL OMP_SET_LOCK(self%lock)
         CALL self%listPart_in%add(part)
+        self%totalWeight = self%totalWeight + part%weight
         CALL OMP_UNSET_LOCK(self%lock)
 
       ELSE
@@ -525,28 +526,29 @@ MODULE moduleMeshCyl
       USE moduleCollisions
       USE moduleSpecies
       USE moduleList
+      use moduleRefParam
       IMPLICIT NONE
 
       CLASS(meshVolCyl), INTENT(inout):: self
-      INTEGER:: Npart !Number of particles inside the cell
-      REAL(8):: Fn !Specific weight
-      REAL(8):: Pmax !Maximum probability of collision
+      INTEGER:: nPart !Number of particles inside the cell
+      REAL(8):: pMax !Maximum probability of collision
       INTEGER:: rnd !random index
       TYPE(particle), POINTER:: part_i, part_j
       INTEGER:: n !collision
       INTEGER:: ij, k
       REAL(8):: sigmaVrelMaxNew
 
-      Fn = species(1)%obj%weight!TODO: Check how to do this for multiple species
-      Npart = self%listPart_in%amount
-      Pmax = Fn*self%sigmaVrelMax*tau/self%volume
-      self%nColl = INT(REAL(Npart*(Npart-1))*Pmax*0.5D0)
+      self%nColl = 0
+      nPart = self%listPart_in%amount
+      IF (nPart > 1) THEN
+        pMax = self%totalWeight*self%sigmaVrelMax*tau/self%volume
+        self%nColl = INT(REAL(nPart)*pMax*0.5D0)
 
-      DO n = 1, self%NColl
+        DO n = 1, self%nColl
           !Select random numbers
-        rnd = 1 + FLOOR(Npart*RAND())
+          rnd = 1 + FLOOR(nPart*RAND())
           part_i => self%listPart_in%get(rnd)
-        rnd = 1 + FLOOR(Npart*RAND())
+          rnd = 1 + FLOOR(nPart*RAND())
           part_j => self%listPart_in%get(rnd)
           ij = interactionIndex(part_i%pt, part_j%pt)
           sigmaVrelMaxNew = 0.D0
@@ -563,6 +565,10 @@ MODULE moduleMeshCyl
             
         END DO
 
+      END IF
+
+      self%totalWeight = 0.D0
+
       !Reset output in nodes
       CALL self%resetOutput()