fm: Add comment to cp_fm_init_random about its RNG seed

cp2k · Nov 20, 2021 · cd2af72 · cd2af72
1 parent 11fe790
commit cd2af72
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/src/fm/cp_fm_types.F b/src/fm/cp_fm_types.F
@@ -346,6 +346,12 @@ SUBROUTINE cp_fm_init_random(matrix, ncol, start_col)
       DEALLOCATE (buff)
 
       ! store seed before deletion (unclear if this is the proper seed)
+
+      ! Note that, the initial state (rng%ig) instead of the current state (rng%cg) is stored in the
+      ! seed variable. As a consequence, each invocation of cp_fm_init_random uses exactly the same
+      ! stream of random numbers. While this seems odd and contrary to the original design,
+      ! it was probably introduced to improve reproducibility.
+      ! See also https://github.com/cp2k/cp2k/pull/506
       CALL rng%get(ig=seed)
 
       CALL timestop(handle)