From f648d86bec9ec2bc0915acb670eb3c76c45d35c4 Mon Sep 17 00:00:00 2001
From: Marilena Bandieramonte <marilena.bandieramonte@cern.ch>
Date: Mon, 16 Nov 2020 11:14:47 +0100
Subject: [PATCH] Use always the same random number seed for the Pythia
generator, to make the simulation reproducible - benchmarking purposes
---
FullSimLight/src/PythiaPrimaryGeneratorAction.cc | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/FullSimLight/src/PythiaPrimaryGeneratorAction.cc b/FullSimLight/src/PythiaPrimaryGeneratorAction.cc
index c840ed9af..37aecd0ab 100644
--- a/FullSimLight/src/PythiaPrimaryGeneratorAction.cc
+++ b/FullSimLight/src/PythiaPrimaryGeneratorAction.cc
@@ -57,6 +57,19 @@ PythiaPrimaryGeneratorAction::PythiaPrimaryGeneratorAction() {
if (access(config, R_OK) == 0) {
pythia.readFile(config);
} else {
+ /*
+ flag name="Pythia:setSeed" default="off"
+ Indicates whether a user-set seed should be used every time the Pythia::init routine is called. If off, the random number generator is initialized with its default seed at the beginning of the run, and never again. If on, each new Pythia::init call (should several be made in the same run) results in the random number being re-initialized, thereby possibly starting over with the same sequence, if you do not watch out.
+
+ mode name="Pythia:seed" default="-1" max="900000000"
+ The seed to be used, if setSeed is on.
+ A negative value gives the default seed,
+ a value 0 gives a random seed based on the time, and
+ a value between 1 and 900,000,000 a unique different random number sequence.
+ */
+ pythia.readString("Random:setSeed = on");
+ // use a reproducible seed: always the same results for benchmarks.
+ pythia.readString("Random:seed = 1234");
for (const auto str : pythia_defaults)
pythia.readString(str);
--
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