whatcanGOwrong
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//go:build ignore
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// +build ignore
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/*
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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* Neither the name of "The Computer Language Benchmarks Game" nor the
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name of "The Computer Language Shootout Benchmarks" nor the names of
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its contributors may be used to endorse or promote products derived
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from this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.
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*/
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/* The Computer Language Benchmarks Game
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* http://shootout.alioth.debian.org/
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*
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* contributed by The Go Authors.
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* based on C program by Christoph Bauer
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*/
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package main
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import (
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"flag"
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"fmt"
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"math"
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)
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var n = flag.Int("n", 1000, "number of iterations")
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type Body struct {
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x, y, z, vx, vy, vz, mass float64
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}
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const (
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solarMass = 4 * math.Pi * math.Pi
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daysPerYear = 365.24
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)
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func (b *Body) offsetMomentum(px, py, pz float64) {
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b.vx = -px / solarMass
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b.vy = -py / solarMass
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b.vz = -pz / solarMass
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}
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type System []*Body
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func NewSystem(body []Body) System {
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n := make(System, len(body))
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for i := 0; i < len(body); i++ {
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n[i] = new(Body) // copy to avoid overwriting the inputs
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*n[i] = body[i]
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}
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var px, py, pz float64
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for _, body := range n {
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px += body.vx * body.mass
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py += body.vy * body.mass
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pz += body.vz * body.mass
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}
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n[0].offsetMomentum(px, py, pz)
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return n
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}
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func (sys System) energy() float64 {
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var e float64
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for i, body := range sys {
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e += 0.5 * body.mass *
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(body.vx*body.vx + body.vy*body.vy + body.vz*body.vz)
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for j := i + 1; j < len(sys); j++ {
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body2 := sys[j]
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dx := body.x - body2.x
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dy := body.y - body2.y
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dz := body.z - body2.z
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distance := math.Sqrt(dx*dx + dy*dy + dz*dz)
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e -= (body.mass * body2.mass) / distance
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}
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}
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return e
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}
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func (sys System) advance(dt float64) {
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for i, body := range sys {
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for j := i + 1; j < len(sys); j++ {
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body2 := sys[j]
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dx := body.x - body2.x
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dy := body.y - body2.y
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dz := body.z - body2.z
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dSquared := dx*dx + dy*dy + dz*dz
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distance := math.Sqrt(dSquared)
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mag := dt / (dSquared * distance)
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body.vx -= dx * body2.mass * mag
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body.vy -= dy * body2.mass * mag
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body.vz -= dz * body2.mass * mag
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body2.vx += dx * body.mass * mag
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body2.vy += dy * body.mass * mag
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body2.vz += dz * body.mass * mag
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}
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}
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for _, body := range sys {
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body.x += dt * body.vx
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body.y += dt * body.vy
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body.z += dt * body.vz
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}
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}
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var (
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jupiter = Body{
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x: 4.84143144246472090e+00,
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y: -1.16032004402742839e+00,
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z: -1.03622044471123109e-01,
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vx: 1.66007664274403694e-03 * daysPerYear,
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vy: 7.69901118419740425e-03 * daysPerYear,
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vz: -6.90460016972063023e-05 * daysPerYear,
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mass: 9.54791938424326609e-04 * solarMass,
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}
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saturn = Body{
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x: 8.34336671824457987e+00,
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y: 4.12479856412430479e+00,
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z: -4.03523417114321381e-01,
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vx: -2.76742510726862411e-03 * daysPerYear,
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vy: 4.99852801234917238e-03 * daysPerYear,
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vz: 2.30417297573763929e-05 * daysPerYear,
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mass: 2.85885980666130812e-04 * solarMass,
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}
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uranus = Body{
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x: 1.28943695621391310e+01,
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y: -1.51111514016986312e+01,
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z: -2.23307578892655734e-01,
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vx: 2.96460137564761618e-03 * daysPerYear,
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vy: 2.37847173959480950e-03 * daysPerYear,
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vz: -2.96589568540237556e-05 * daysPerYear,
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mass: 4.36624404335156298e-05 * solarMass,
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}
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neptune = Body{
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x: 1.53796971148509165e+01,
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y: -2.59193146099879641e+01,
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z: 1.79258772950371181e-01,
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vx: 2.68067772490389322e-03 * daysPerYear,
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vy: 1.62824170038242295e-03 * daysPerYear,
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vz: -9.51592254519715870e-05 * daysPerYear,
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mass: 5.15138902046611451e-05 * solarMass,
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}
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sun = Body{
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mass: solarMass,
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}
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)
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func main() {
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flag.Parse()
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system := NewSystem([]Body{sun, jupiter, saturn, uranus, neptune})
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fmt.Printf("%.9f\n", system.energy())
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for i := 0; i < *n; i++ {
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system.advance(0.01)
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}
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fmt.Printf("%.9f\n", system.energy())
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}
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