From cb909adf60aa10d4b3532f3786e9cabeda3e5c6a Mon Sep 17 00:00:00 2001
From: "armindamon.riess" <armindamon.riess@uzh.ch>
Date: Wed, 30 Nov 2022 14:26:34 +0100
Subject: [PATCH] greatly increased speed of force calculation
---
lib/nBodySim.cpp | 39 ++++++++++++++++++++++++++++++++++++++-
1 file changed, 38 insertions(+), 1 deletion(-)
diff --git a/lib/nBodySim.cpp b/lib/nBodySim.cpp
index b2eca9d..adb2980 100644
--- a/lib/nBodySim.cpp
+++ b/lib/nBodySim.cpp
@@ -61,7 +61,43 @@ void nBodySim::runSimulation(double dt, unsigned nSteps) {
updatePositions(dt);
}
}
-
+///*
+void nBodySim::calculateForces() {
+ #pragma omp parallel for
+ for (unsigned i=0; i < 3*nParticles_; ++i) {
+ forces_[i] = 0.0;
+ }
+ // loop over each pair of particles and calculate the force between them
+ #pragma omp parallel for
+ for (unsigned i = 0; i < nParticles_; i++) {
+ for (unsigned j = i+1; j < nParticles_; j++) {
+ // calculate distance between particles
+ double dx = positions_[3*j] - positions_[3*i];
+ double dy = positions_[3*j+1] - positions_[3*i+1];
+ double dz = positions_[3*j+2] - positions_[3*i+2];
+ double r2 = dx*dx + dy*dy + dz*dz;
+ double r = std::sqrt(r2);
+ dx /= r;
+ dy /= r;
+ dz /= r;
+ // calculate force
+ double mi = masses_[i];
+ double mj = masses_[j];
+ double s = softening_[i];
+ double fx = mi*mj * dx / (r2 + s*s);
+ double fy = mi*mj * dy / (r2 + s*s);
+ double fz = mi*mj * dz / (r2 + s*s);
+ forces_[3*i] += fx;
+ forces_[3*i+1] += fy;
+ forces_[3*i+2] += fz;
+ forces_[3*j] -= fx;
+ forces_[3*j+1] -= fy;
+ forces_[3*j+2] -= fz;
+ }
+ }
+}
+//*/
+/*
void nBodySim::calculateForces() {
#pragma omp parallel for
for (unsigned i=0; i < 3*nParticles_; ++i) {
@@ -91,6 +127,7 @@ void nBodySim::calculateForces() {
}
}
}
+*/
void nBodySim::updatePositions(double dt) {
#pragma omp parallel for
--
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