Fix injection

Half-Maxwellian distribution should inject particles correctly

src/modules/common/moduleRandom.f90

@@ -66,6 +66,23 @@ MODULE moduleRandom
 
     END FUNCTION randomMaxwellian
 
+    !Returns a random number in a Maxwellian distribution of mean 0 and width 1
+    FUNCTION randomHalfMaxwellian() RESULT(rnd)
+      IMPLICIT NONE
+
+      REAL(8):: rnd
+      REAL(8):: x
+
+      rnd = 0.D0
+      x = 0.D0
+      DO WHILE (x == 0.D0)
+        CALL RANDOM_NUMBER(x)
+      END DO
+
+      rnd = DSQRT(-DLOG(x))
+
+    END FUNCTION randomHalfMaxwellian
+
     !Returns a random number weighted with the cumWeight array
     FUNCTION randomWeighted(cumWeight, sumWeight) RESULT(rnd)
       IMPLICIT NONE