From 838bb351fcf7ac6b75287475eedb898f508a8843 Mon Sep 17 00:00:00 2001
From: Paul Romano <romano7@gmail.com>
Date: Mon, 19 Mar 2012 14:07:27 -0400
Subject: [PATCH] Added option to change random number seed based on
 cmfd_parallel branch.

---
 docs/source/usersguide/input.rst         | 8 ++++++++
 src/global.F90                           | 3 +++
 src/initialize.F90                       | 6 +++---
 src/input_xml.F90                        | 4 ++++
 src/random_lcg.F90                       | 4 +++-
 src/xml-fortran/templates/settings_t.xml | 1 +
 6 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/docs/source/usersguide/input.rst b/docs/source/usersguide/input.rst
index 55072f24fa..3e0aec34e7 100644
--- a/docs/source/usersguide/input.rst
+++ b/docs/source/usersguide/input.rst
@@ -404,6 +404,14 @@ sub-elements and can be set to either "off" or "on".
 
   *Default*: on
 
+``seed`` Element
+----------------
+
+The ``seed`` element is used to set the seed used for the linear congruential
+pseudo-random number generator.
+
+  *Default*: 1
+
 ``source`` Element
 ------------------
 
diff --git a/src/global.F90 b/src/global.F90
index c64ebedc9d..5fadb2e1af 100644
--- a/src/global.F90
+++ b/src/global.F90
@@ -211,6 +211,9 @@ module global
   ! Message used in message/warning/fatal_error
   character(MAX_LINE_LEN) :: message
 
+  ! Random number seed
+  integer(8) :: seed = 1_8
+
   ! Problem type
   integer :: problem_type = PROB_CRITICALITY
 
diff --git a/src/initialize.F90 b/src/initialize.F90
index 3d3719b48d..3275c1c282 100644
--- a/src/initialize.F90
+++ b/src/initialize.F90
@@ -72,15 +72,15 @@ contains
        call header("INITIALIZATION", level=1)
     end if
 
-    ! Initialize random number generator
-    call initialize_prng()
-
     ! set up dictionaries
     call create_dictionaries()
 
     ! Read XML input files
     call read_input_xml()
 
+    ! Initialize random number generator
+    call initialize_prng()
+
     ! Set up universe structures
     call prepare_universes()
 
diff --git a/src/input_xml.F90 b/src/input_xml.F90
index c1257855e1..2837fd1ebf 100644
--- a/src/input_xml.F90
+++ b/src/input_xml.F90
@@ -68,6 +68,7 @@ contains
     cross_sections_ = ""
     verbosity_ = 0
     energy_grid_ = "union"
+    seed_ = 0_8
 
     ! Parse settings.xml file
     call read_xml_file_settings_t(filename)
@@ -112,6 +113,9 @@ contains
        call fatal_error()
     end if
 
+    ! Copy random number seed if specified
+    if (seed_ > 0) seed = seed_
+
     ! Energy grid methods
     select case (energy_grid_)
     case ('nuclide')
diff --git a/src/random_lcg.F90 b/src/random_lcg.F90
index 674be52122..694885c013 100644
--- a/src/random_lcg.F90
+++ b/src/random_lcg.F90
@@ -49,7 +49,9 @@ contains
 
   subroutine initialize_prng()
 
-    prn_seed0  = 1_8
+    use global, only: seed
+
+    prn_seed0  = seed
     prn_seed   = prn_seed
     prn_mult   = 2806196910506780709_8
     prn_add    = 1_8
diff --git a/src/xml-fortran/templates/settings_t.xml b/src/xml-fortran/templates/settings_t.xml
index 4b450f5724..dbe8bd6226 100644
--- a/src/xml-fortran/templates/settings_t.xml
+++ b/src/xml-fortran/templates/settings_t.xml
@@ -32,6 +32,7 @@
   <variable name="energy_grid_" tag="energy_grid" type="word" length="7" />
   <variable name="entropy_" tag="entropy" type="entropy_xml" dimension="1" />
   <variable name="ptables_" tag="ptables" type="word" length="3" />
+  <variable name="seed_" tag="seed" type="integer" />
   <variable name="source_" tag="source" type="source_xml" />
   <variable name="survival_" tag="survival_biasing" type="word" length="3" />
   <variable name="verbosity_" tag="verbosity" type="integer" />