From 1828f66f16a0d5be513c2ccd08aa8f6b31fd8618 Mon Sep 17 00:00:00 2001
From: James Willis <james.s.willis@durham.ac.uk>
Date: Mon, 25 Apr 2016 16:27:22 +0100
Subject: [PATCH] Added function to shuffle an array of particles randomly.
Moved random_uniform from testPair/test27cells to tools.c.
---
src/tools.c | 30 ++++++++++++++++++++++++++++++
src/tools.h | 3 +++
2 files changed, 33 insertions(+)
diff --git a/src/tools.c b/src/tools.c
index d25b7401a1..8fc393144f 100644
--- a/src/tools.c
+++ b/src/tools.c
@@ -471,3 +471,33 @@ void engine_single_force(double *dim, long long int pid,
p.a_hydro[1], p.a_hydro[2]);
fflush(stdout);
}
+
+/**
+ * Returns a random number (uniformly distributed) in [a,b[
+ */
+double random_uniform(double a, double b) {
+ return (rand() / (double)RAND_MAX) * (b - a) + a;
+}
+
+/**
+ * @brief Randomly shuffle an array of particles.
+ */
+void shuffle_particles(struct part *parts, const int count) {
+
+ if(count > 1) {
+
+ for(int i=0; i<count - 1; i++) {
+
+ int j = i + random_uniform(0.,(double)(count - 1 - i));
+
+ struct part particle = parts[j];
+
+ parts[j] = parts[i];
+
+ parts[i] = particle;
+ }
+
+ }
+ else error("Array not big enough to shuffle!");
+
+}
diff --git a/src/tools.h b/src/tools.h
index ccffc77ceb..8e02126529 100644
--- a/src/tools.h
+++ b/src/tools.h
@@ -38,4 +38,7 @@ void self_all_density(struct runner *r, struct cell *ci);
void pairs_n2(double *dim, struct part *__restrict__ parts, int N,
int periodic);
+double random_uniform(double a, double b);
+void shuffle_particles(struct part *parts, const int count);
+
#endif /* SWIFT_TOOL_H */
--
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