I am reading the book, Exploring Raspberry Pi - Interfacing to the Real World with Embedded Linux by Derek Molloy. In Chapter 5, Programming on the Raspberry Pi, the author does a speed test to compare different languages (see the image). I will list my version of his C++ program below (with the C++ code commented out).

Here are my results [running on a Raspberry Pi 3, Rasbian, 32-bit Julia] - which are not bad - better than 1/2 of them, but I think it can be better.

```
julia-user@NODE-RPI3:~/julia-0.6.0/bin $ ./julia n-body.jl
-0.169075164
-0.169083134
20.172162 seconds (38.14 k allocations: 1.559 MiB)
```

Here is the program (again - C++ simply commented out).

```
#/* The Computer Language Benchmarks Game
# * http://benchmarksgame.alioth.debian.org/
# *
# * contributed by Christoph Bauer
# *
# */
##include <math.h>
##include <stdio.h>
##include <stdlib.h>
##define pi 3.141592653589793
##define solar_mass (4 * pi * pi)
##define days_per_year 365.24
const pi = 3.141592653589793
const solar_mass = (4 * pi * pi)
const days_per_year = 365.24
#struct planet {
# double x, y, z;
# double vx, vy, vz;
# double mass;
#};
mutable struct planet
x::Float64
y::Float64
z::Float64
vx::Float64
vy::Float64
vz::Float64
mass::Float64
end
#void advance(int nbodies, struct planet * bodies, double dt)
#{
# int i, j;
#
# for (i = 0; i < nbodies; i++) {
# struct planet * b = &(bodies[i]);
# for (j = i + 1; j < nbodies; j++) {
# struct planet * b2 = &(bodies[j]);
# double dx = b->x - b2->x;
# double dy = b->y - b2->y;
# double dz = b->z - b2->z;
# double distance = sqrt(dx * dx + dy * dy + dz * dz);
# double mag = dt / (distance * distance * distance);
# b->vx -= dx * b2->mass * mag;
# b->vy -= dy * b2->mass * mag;
# b->vz -= dz * b2->mass * mag;
# b2->vx += dx * b->mass * mag;
# b2->vy += dy * b->mass * mag;
# b2->vz += dz * b->mass * mag;
# }
# }
# for (i = 0; i < nbodies; i++) {
# struct planet * b = &(bodies[i]);
# b->x += dt * b->vx;
# b->y += dt * b->vy;
# b->z += dt * b->vz;
# }
#}
function advance(nbodies::Int, bodies::Vector{planet}, dt::Float64)
for i = 1:nbodies
b::planet = bodies[i]
for j = i + 1: nbodies
b2::planet = bodies[j]
dx::Float64 = b.x - b2.x
dy::Float64 = b.y - b2.y
dz::Float64 = b.z - b2.z
distance::Float64 = sqrt(dx * dx + dy * dy + dz * dz)
mag::Float64 = dt / (distance * distance * distance)
b.vx -= dx * b2.mass * mag
b.vy -= dy * b2.mass * mag
b.vz -= dz * b2.mass * mag
b2.vx += dx * b.mass * mag
b2.vy += dy * b.mass * mag
b2.vz += dz * b.mass * mag
end
end
for i = 1:nbodies
b::planet = bodies[i]
b.x += dt * b.vx
b.y += dt * b.vy
b.z += dt * b.vz
end
end
#double energy(int nbodies, struct planet * bodies)
#{
# double e;
# int i, j;
#
# e = 0.0;
# for (i = 0; i < nbodies; i++) {
# struct planet * b = &(bodies[i]);
# e += 0.5 * b->mass * (b->vx * b->vx + b->vy * b->vy + b->vz * b->vz);
# for (j = i + 1; j < nbodies; j++) {
# struct planet * b2 = &(bodies[j]);
# double dx = b->x - b2->x;
# double dy = b->y - b2->y;
# double dz = b->z - b2->z;
# double distance = sqrt(dx * dx + dy * dy + dz * dz);
# e -= (b->mass * b2->mass) / distance;
# }
# }
# return e;
#}
function energy(nbodies::Int, bodies::Vector{planet})
e::Float64 = 0.0
for i = 1:nbodies
b::planet = bodies[i]
e += 0.5 * b.mass * (b.vx * b.vx + b.vy * b.vy + b.vz * b.vz)
for j = i + 1:nbodies
b2::planet = bodies[j]
dx::Float64 = b.x - b2.x
dy::Float64 = b.y - b2.y
dz::Float64 = b.z - b2.z
distance::Float64 = sqrt(dx * dx + dy * dy + dz * dz)
e -= (b.mass * b2.mass) / distance
end
end
return e
end
#void offset_momentum(int nbodies, struct planet * bodies)
#{
# double px = 0.0, py = 0.0, pz = 0.0;
# int i;
# for (i = 0; i < nbodies; i++) {
# px += bodies[i].vx * bodies[i].mass;
# py += bodies[i].vy * bodies[i].mass;
# pz += bodies[i].vz * bodies[i].mass;
# }
# bodies[0].vx = - px / solar_mass;
# bodies[0].vy = - py / solar_mass;
# bodies[0].vz = - pz / solar_mass;
#}
function offset_momentum(nbodies::Int, bodies::Vector{planet})
px::Float64 = 0.0
py::Float64 = 0.0
pz::Float64 = 0.0
for i = 1:nbodies
px += bodies[i].vx * bodies[i].mass
py += bodies[i].vy * bodies[i].mass
pz += bodies[i].vz * bodies[i].mass
end
bodies[1].vx = - px / solar_mass
bodies[1].vy = - py / solar_mass
bodies[1].vz = - pz / solar_mass
end
##define NBODIES 5
const NBODIES = 5
#struct planet bodies[NBODIES] = {
# { /* sun */
# 0, 0, 0, 0, 0, 0, solar_mass
# },
# { /* jupiter */
# 4.84143144246472090e+00,
# -1.16032004402742839e+00,
# -1.03622044471123109e-01,
# 1.66007664274403694e-03 * days_per_year,
# 7.69901118419740425e-03 * days_per_year,
# -6.90460016972063023e-05 * days_per_year,
# 9.54791938424326609e-04 * solar_mass
# },
# { /* saturn */
# 8.34336671824457987e+00,
# 4.12479856412430479e+00,
# -4.03523417114321381e-01,
# -2.76742510726862411e-03 * days_per_year,
# 4.99852801234917238e-03 * days_per_year,
# 2.30417297573763929e-05 * days_per_year,
# 2.85885980666130812e-04 * solar_mass
# },
# { /* uranus */
# 1.28943695621391310e+01,
# -1.51111514016986312e+01,
# -2.23307578892655734e-01,
# 2.96460137564761618e-03 * days_per_year,
# 2.37847173959480950e-03 * days_per_year,
# -2.96589568540237556e-05 * days_per_year,
# 4.36624404335156298e-05 * solar_mass
# },
# { /* neptune */
# 1.53796971148509165e+01,
# -2.59193146099879641e+01,
# 1.79258772950371181e-01,
# 2.68067772490389322e-03 * days_per_year,
# 1.62824170038242295e-03 * days_per_year,
# -9.51592254519715870e-05 * days_per_year,
# 5.15138902046611451e-05 * solar_mass
# }
#};
bodies = Vector{planet}(NBODIES)
bodies[1] = planet( # sun
0, 0, 0, 0, 0, 0, solar_mass
)
bodies[2] = planet( #jupiter
4.84143144246472090e+00,
-1.16032004402742839e+00,
-1.03622044471123109e-01,
1.66007664274403694e-03 * days_per_year,
7.69901118419740425e-03 * days_per_year,
-6.90460016972063023e-05 * days_per_year,
9.54791938424326609e-04 * solar_mass
)
bodies[3] = planet( #saturn
8.34336671824457987e+00,
4.12479856412430479e+00,
-4.03523417114321381e-01,
-2.76742510726862411e-03 * days_per_year,
4.99852801234917238e-03 * days_per_year,
2.30417297573763929e-05 * days_per_year,
2.85885980666130812e-04 * solar_mass
)
bodies[4] = planet( #uranus
1.28943695621391310e+01,
-1.51111514016986312e+01,
-2.23307578892655734e-01,
2.96460137564761618e-03 * days_per_year,
2.37847173959480950e-03 * days_per_year,
-2.96589568540237556e-05 * days_per_year,
4.36624404335156298e-05 * solar_mass
)
bodies[5] = planet( #neptune
1.53796971148509165e+01,
-2.59193146099879641e+01,
1.79258772950371181e-01,
2.68067772490389322e-03 * days_per_year,
1.62824170038242295e-03 * days_per_year,
-9.51592254519715870e-05 * days_per_year,
5.15138902046611451e-05 * solar_mass
)
#int main(int argc, char ** argv)
#{
# int n = atoi(argv[1]);
# int i;
#
# offset_momentum(NBODIES, bodies);
# printf ("%.9f\n", energy(NBODIES, bodies));
# for (i = 1; i <= n; i++)
# advance(NBODIES, bodies, 0.01);
# printf ("%.9f\n", energy(NBODIES, bodies));
# return 0;
#}
function main(iterations::Int)
n::Int = iterations
offset_momentum(NBODIES, bodies);
@printf("%.9f\n", energy(NBODIES, bodies))
for i = 1:n
advance(NBODIES, bodies, 0.01)
end
@printf("%.9f\n", energy(NBODIES, bodies))
end
@time main(5000000)
```

BTW - on my Dell Optiplex 755 Intel Dual Core E6580 @ 3 GHz (Debian 9.1 - kernel 4.9) - my results ranked about the same on the chart.

```
julia-user@NODE-DELL755:~/julia-0.6.0/bin$ ./julia n-body.jl
-0.169075164
-0.169083134
2.132114 seconds (38.14 k allocations: 1.557 MiB)
```