From eef631de500cf9631043c116b80b876d7108210b Mon Sep 17 00:00:00 2001
From: Grzegorz Kowal <grzegorz@amuncode.org>
Date: Fri, 9 Feb 2018 16:44:19 -0200
Subject: [PATCH] RANDOM: Rewrite seed numbers handling.

The array of seed numbers makes sense only when OpenMP is used. With
MPI on, the length of seed vector on each MPI process is equal to the
number of OpenMP threads. For no OpenMP, only one seed number per MPI
process is used.

Signed-off-by: Grzegorz Kowal <grzegorz@amuncode.org>
---
 src/driver.F90 |  5 ++--
 src/random.F90 | 70 ++++++++++++++++++--------------------------------
 2 files changed, 28 insertions(+), 47 deletions(-)

diff --git a/src/driver.F90 b/src/driver.F90
index cbf20b5..ee37f85 100644
--- a/src/driver.F90
+++ b/src/driver.F90
@@ -308,9 +308,10 @@ program amun
 !
   call setup_mpi(div(:), per(:), .false.)
 
-! initialize the random number generator
+! initialize the random number generator (passes the number of OpenMP threads
+! and the current thread number)
 !
-  call initialize_random(nprocs, nproc)
+  call initialize_random(1, 0)
 
 ! initialize geometry modules and print info
 !
diff --git a/src/random.F90 b/src/random.F90
index 451dbb2..14790f1 100644
--- a/src/random.F90
+++ b/src/random.F90
@@ -80,7 +80,7 @@ module random
 !
 !===============================================================================
 !
-  subroutine initialize_random(nprocs, nproc)
+  subroutine initialize_random(nthreads, nthread)
 
 ! obtain required variables from other modules
 !
@@ -92,7 +92,7 @@ module random
 
 ! subroutine arguments
 !
-    integer, intent(in) :: nprocs, nproc
+    integer, intent(in) :: nthreads, nthread
 
 ! local variables
 !
@@ -112,9 +112,9 @@ module random
     call start_timer(iri)
 #endif /* PROFILE */
 
-! set the processor number
+! set the thread number
 !
-    kp = nproc
+    kp = nthread
 
 ! obtain the generator type
 !
@@ -122,7 +122,7 @@ module random
 
 ! calculate the number of seeds
 !
-    nseeds = 2 * nprocs
+    nseeds = nthreads
     lseed  = nseeds - 1
 
 ! allocate seeds for random number generator
@@ -138,12 +138,8 @@ module random
         seeds(i) = 123456789 * r
       end do
     case default
-      call random_number(r)
-      do i = 0, nprocs - 1
-        seeds(i) = 123456789 * r
-      end do
-      call random_number(r)
-      do i = nprocs, lseed
+      r = 0.1234567890123456789
+      do i = 0, lseed
         seeds(i) = 123456789 * r
       end do
     end select
@@ -204,7 +200,7 @@ module random
 !
 !===============================================================================
 !
-  subroutine set_seeds(np, seed)
+  subroutine set_seeds(np, nseeds)
 
 ! declare all variables as implicit
 !
@@ -212,8 +208,8 @@ module random
 
 ! input arguments
 !
-    integer                           , intent(in) :: np
-    integer(kind=4), dimension(0:np-1), intent(in) :: seed
+    integer                       , intent(in) :: np
+    integer(kind=4), dimension(np), intent(in) :: nseeds
 
 ! local variables
 !
@@ -230,35 +226,19 @@ module random
 
 ! set the seeds only if the input array and seeds have the same sizes
 !
-    if (np == nseeds) then
-
-      seeds(0:lseed) = seed(0:lseed)
-
-    else
-
-! if the input array and seeds have different sizes, expand or shrink seeds
-!
-      select case(gentype)
-      case('random')
-        l = min(lseed, np - 1)
-        seeds(0:l) = seed(0:l)
-        if (l < lseed) then
-          do i = l + 1, lseed
-            call random_number(r)
-            seeds(i) = 123456789 * r
-          end do
-        end if
-      case default
-        l = nseeds / 2
-        do i = 0, l - 1
-          seeds(i) = seed(0)
+    l = min(lseed, np - 1)
+    seeds(0:l) = seed(1:l+1)
+    select case(gentype)
+    case('random')
+      if (l < lseed) then
+        do i = l + 1, lseed
+          call random_number(r)
+          seeds(i) = 123456789 * r
         end do
-        do i = l, lseed
-          seeds(i) = seed(np-1)
-        end do
-      end select
-
-    end if
+      end if
+    case default
+      seeds(l+1:lseed) = seeds(0)
+    end select
 
 #ifdef PROFILE
 ! stop accounting time for the random number generator
@@ -279,7 +259,7 @@ module random
 !
 !===============================================================================
 !
-  subroutine get_seeds(seed)
+  subroutine get_seeds(rseeds)
 
 ! declare all variables as implicit
 !
@@ -287,7 +267,7 @@ module random
 
 ! output arguments
 !
-    integer(kind=4), dimension(0:lseed), intent(out) :: seed
+    integer(kind=4), dimension(nseeds), intent(out) :: rseeds
 !
 !-------------------------------------------------------------------------------
 !
@@ -297,7 +277,7 @@ module random
     call start_timer(iri)
 #endif /* PROFILE */
 
-    seed(0:lseed) = seeds(0:lseed)
+    rseeds(1:nseeds) = seeds(0:lseed)
 
 #ifdef PROFILE
 ! stop accounting time for the random number generator