159 lines
5.6 KiB
Scheme
159 lines
5.6 KiB
Scheme
#!/usr/bin/mzscheme -qu
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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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;; Imperative-style implementation based on the SBCL implementation by
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;; Patrick Frankenberger and Juho Snellman, but using only native Scheme
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;; idioms like 'named let' and 'do' special form.
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;;
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;; Contributed by Anthony Borla, then converted for mzscheme
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;; by Matthew Flatt and Brent Fulgham
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#|
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Correct output N = 1000 is
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-0.169075164
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-0.169087605
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|#
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#lang scheme/base
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(require scheme/cmdline
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scheme/flonum)
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;; ------------------------------
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;; define planetary masses, initial positions & velocity
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(define +pi+ 3.141592653589793)
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(define +days-per-year+ 365.24)
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(define +solar-mass+ (* 4 +pi+ +pi+))
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(define +dt+ 0.01)
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(define-struct body (x y z vx vy vz mass)
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#:mutable)
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(define *sun*
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(make-body 0.0 0.0 0.0 0.0 0.0 0.0 +solar-mass+))
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(define *jupiter*
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(make-body 4.84143144246472090
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-1.16032004402742839
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-1.03622044471123109e-1
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(* 1.66007664274403694e-3 +days-per-year+)
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(* 7.69901118419740425e-3 +days-per-year+)
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(* -6.90460016972063023e-5 +days-per-year+)
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(* 9.54791938424326609e-4 +solar-mass+)))
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(define *saturn*
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(make-body 8.34336671824457987
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4.12479856412430479
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-4.03523417114321381e-1
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(* -2.76742510726862411e-3 +days-per-year+)
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(* 4.99852801234917238e-3 +days-per-year+)
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(* 2.30417297573763929e-5 +days-per-year+)
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(* 2.85885980666130812e-4 +solar-mass+)))
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(define *uranus*
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(make-body 1.28943695621391310e1
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-1.51111514016986312e1
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-2.23307578892655734e-1
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(* 2.96460137564761618e-03 +days-per-year+)
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(* 2.37847173959480950e-03 +days-per-year+)
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(* -2.96589568540237556e-05 +days-per-year+)
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(* 4.36624404335156298e-05 +solar-mass+)))
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(define *neptune*
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(make-body 1.53796971148509165e+01
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-2.59193146099879641e+01
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1.79258772950371181e-01
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(* 2.68067772490389322e-03 +days-per-year+)
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(* 1.62824170038242295e-03 +days-per-year+)
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(* -9.51592254519715870e-05 +days-per-year+)
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(* 5.15138902046611451e-05 +solar-mass+)))
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(define *system* (list *sun* *jupiter* *saturn* *uranus* *neptune*))
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;; -------------------------------
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(define (offset-momentum)
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(let loop-i ([i *system*] [px 0.0] [py 0.0] [pz 0.0])
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(if (null? i)
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(begin
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(set-body-vx! (car *system*) (fl/ (fl- 0.0 px) +solar-mass+))
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(set-body-vy! (car *system*) (fl/ (fl- 0.0 py) +solar-mass+))
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(set-body-vz! (car *system*) (fl/ (fl- 0.0 pz) +solar-mass+)))
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(let ([i1 (car i)])
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(loop-i (cdr i)
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(fl+ px (fl* (body-vx i1) (body-mass i1)))
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(fl+ py (fl* (body-vy i1) (body-mass i1)))
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(fl+ pz (fl* (body-vz i1) (body-mass i1))))))))
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;; -------------------------------
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(define (energy)
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(let loop-o ([o *system*] [e 0.0])
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(if (null? o)
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e
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(let* ([o1 (car o)]
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[e (+ e (fl* 0.5
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(fl* (body-mass o1)
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(fl+ (fl+ (fl* (body-vx o1) (body-vx o1))
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(fl* (body-vy o1) (body-vy o1)))
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(fl* (body-vz o1) (body-vz o1))))))])
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(let loop-i ([i (cdr o)] [e e])
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(if (null? i)
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(loop-o (cdr o) e)
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(let* ([i1 (car i)]
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[dx (fl- (body-x o1) (body-x i1))]
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[dy (fl- (body-y o1) (body-y i1))]
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[dz (fl- (body-z o1) (body-z i1))]
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[dist (flsqrt (fl+ (fl+ (fl* dx dx) (fl* dy dy)) (fl* dz dz)))]
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[e (fl- e (fl/ (fl* (body-mass o1) (body-mass i1)) dist))])
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(loop-i (cdr i) e))))))))
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;; -------------------------------
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(define (advance)
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(let loop-o ([o *system*])
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(when (pair? o)
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(let* ([o1 (car o)]
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[o1x (body-x o1)]
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[o1y (body-y o1)]
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[o1z (body-z o1)]
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[om (body-mass o1)])
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(let loop-i ([i (cdr o)]
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[vx (body-vx o1)]
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[vy (body-vy o1)]
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[vz (body-vz o1)])
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(if (pair? i)
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(let* ([i1 (car i)]
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[dx (fl- o1x (body-x i1))]
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[dy (fl- o1y (body-y i1))]
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[dz (fl- o1z (body-z i1))]
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[dist2 (fl+ (fl+ (fl* dx dx) (fl* dy dy)) (fl* dz dz))]
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[mag (fl/ +dt+ (fl* dist2 (flsqrt dist2)))]
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[dxmag (fl* dx mag)]
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[dymag (fl* dy mag)]
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[dzmag (fl* dz mag)]
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[im (body-mass i1)])
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(set-body-vx! i1 (fl+ (body-vx i1) (fl* dxmag om)))
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(set-body-vy! i1 (fl+ (body-vy i1) (fl* dymag om)))
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(set-body-vz! i1 (fl+ (body-vz i1) (fl* dzmag om)))
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(loop-i (cdr i)
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(fl- vx (fl* dxmag im))
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(fl- vy (fl* dymag im))
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(fl- vz (fl* dzmag im))))
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(begin (set-body-vx! o1 vx)
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(set-body-vy! o1 vy)
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(set-body-vz! o1 vz)
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(set-body-x! o1 (fl+ o1x (fl* +dt+ vx)))
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(set-body-y! o1 (fl+ o1y (fl* +dt+ vy)))
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(set-body-z! o1 (fl+ o1z (fl* +dt+ vz)))))))
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(loop-o (cdr o)))))
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;; -------------------------------
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(let ([n (command-line #:args (n) (string->number n))])
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(offset-momentum)
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(printf "~a\n" (real->decimal-string (energy) 9))
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(for ([i (in-range n)]) (advance))
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(printf "~a\n" (real->decimal-string (energy) 9)))
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