1 /* 2 Redistribution and use in source and binary forms, with or without 3 modification, are permitted provided that the following conditions are met: 4 5 * Redistributions of source code must retain the above copyright 6 notice, this list of conditions and the following disclaimer. 7 8 * Redistributions in binary form must reproduce the above copyright 9 notice, this list of conditions and the following disclaimer in the 10 documentation and/or other materials provided with the distribution. 11 12 * Neither the name of "The Computer Language Benchmarks Game" nor the 13 name of "The Computer Language Shootout Benchmarks" nor the names of 14 its contributors may be used to endorse or promote products derived 15 from this software without specific prior written permission. 16 17 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 18 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 21 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 22 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 23 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 24 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 25 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 26 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 27 POSSIBILITY OF SUCH DAMAGE. 28 */ 29 30 /* The Computer Language Benchmarks Game 31 * http://shootout.alioth.debian.org/ 32 * 33 * contributed by The Go Authors. 34 * based on C program by Christoph Bauer 35 */ 36 37 package main 38 39 import ( 40 "flag" 41 "fmt" 42 "math" 43 ) 44 45 var n = flag.Int("n", 1000, "number of iterations") 46 47 type Body struct { 48 x, y, z, vx, vy, vz, mass float64 49 } 50 51 const ( 52 solarMass = 4 * math.Pi * math.Pi 53 daysPerYear = 365.24 54 ) 55 56 func (b *Body) offsetMomentum(px, py, pz float64) { 57 b.vx = -px / solarMass 58 b.vy = -py / solarMass 59 b.vz = -pz / solarMass 60 } 61 62 type System []*Body 63 64 func NewSystem(body []Body) System { 65 n := make(System, len(body)) 66 for i := 0; i < len(body); i++ { 67 n[i] = new(Body) // copy to avoid overwriting the inputs 68 *n[i] = body[i] 69 } 70 var px, py, pz float64 71 for _, body := range n { 72 px += body.vx * body.mass 73 py += body.vy * body.mass 74 pz += body.vz * body.mass 75 } 76 n[0].offsetMomentum(px, py, pz) 77 return n 78 } 79 80 func (sys System) energy() float64 { 81 var e float64 82 for i, body := range sys { 83 e += 0.5 * body.mass * 84 (body.vx*body.vx + body.vy*body.vy + body.vz*body.vz) 85 for j := i + 1; j < len(sys); j++ { 86 body2 := sys[j] 87 dx := body.x - body2.x 88 dy := body.y - body2.y 89 dz := body.z - body2.z 90 distance := math.Sqrt(dx*dx + dy*dy + dz*dz) 91 e -= (body.mass * body2.mass) / distance 92 } 93 } 94 return e 95 } 96 97 func (sys System) advance(dt float64) { 98 for i, body := range sys { 99 for j := i + 1; j < len(sys); j++ { 100 body2 := sys[j] 101 dx := body.x - body2.x 102 dy := body.y - body2.y 103 dz := body.z - body2.z 104 105 dSquared := dx*dx + dy*dy + dz*dz 106 distance := math.Sqrt(dSquared) 107 mag := dt / (dSquared * distance) 108 109 body.vx -= dx * body2.mass * mag 110 body.vy -= dy * body2.mass * mag 111 body.vz -= dz * body2.mass * mag 112 113 body2.vx += dx * body.mass * mag 114 body2.vy += dy * body.mass * mag 115 body2.vz += dz * body.mass * mag 116 } 117 } 118 119 for _, body := range sys { 120 body.x += dt * body.vx 121 body.y += dt * body.vy 122 body.z += dt * body.vz 123 } 124 } 125 126 var ( 127 jupiter = Body{ 128 x: 4.84143144246472090e+00, 129 y: -1.16032004402742839e+00, 130 z: -1.03622044471123109e-01, 131 vx: 1.66007664274403694e-03 * daysPerYear, 132 vy: 7.69901118419740425e-03 * daysPerYear, 133 vz: -6.90460016972063023e-05 * daysPerYear, 134 mass: 9.54791938424326609e-04 * solarMass, 135 } 136 saturn = Body{ 137 x: 8.34336671824457987e+00, 138 y: 4.12479856412430479e+00, 139 z: -4.03523417114321381e-01, 140 vx: -2.76742510726862411e-03 * daysPerYear, 141 vy: 4.99852801234917238e-03 * daysPerYear, 142 vz: 2.30417297573763929e-05 * daysPerYear, 143 mass: 2.85885980666130812e-04 * solarMass, 144 } 145 uranus = Body{ 146 x: 1.28943695621391310e+01, 147 y: -1.51111514016986312e+01, 148 z: -2.23307578892655734e-01, 149 vx: 2.96460137564761618e-03 * daysPerYear, 150 vy: 2.37847173959480950e-03 * daysPerYear, 151 vz: -2.96589568540237556e-05 * daysPerYear, 152 mass: 4.36624404335156298e-05 * solarMass, 153 } 154 neptune = Body{ 155 x: 1.53796971148509165e+01, 156 y: -2.59193146099879641e+01, 157 z: 1.79258772950371181e-01, 158 vx: 2.68067772490389322e-03 * daysPerYear, 159 vy: 1.62824170038242295e-03 * daysPerYear, 160 vz: -9.51592254519715870e-05 * daysPerYear, 161 mass: 5.15138902046611451e-05 * solarMass, 162 } 163 sun = Body{ 164 mass: solarMass, 165 } 166 ) 167 168 func main() { 169 flag.Parse() 170 171 system := NewSystem([]Body{sun, jupiter, saturn, uranus, neptune}) 172 fmt.Printf("%.9f\n", system.energy()) 173 for i := 0; i < *n; i++ { 174 system.advance(0.01) 175 } 176 fmt.Printf("%.9f\n", system.energy()) 177 } 178
