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<a href="/plan9/">Plan 9 from Bell Labs</a>’s /usr/web/sources/contrib/aiju/mole1.c


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Copyright © 2009 Alcatel-Lucent. 
Distributed under the
<a href="/plan9/license.html">Lucent Public License version 1.02</a>.
 
<a href="/plan9/download.html">Download the Plan 9 distribution.</a>

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#include <u.h>
#include <libc.h>
#include <draw.h>
#include <event.h>

enum {N = 20};

#define dt 0.01
#define xmin -40
#define xmax 40
#define ymin -40
#define ymax 40
#define v0 0.2
#define mini(a,b) (((a)<(b))?(a):(b))

typedef struct Particle Particle;
struct Particle {
double x, y;
double vx, vy;
double ax, ay;
double prevx, prevy;
Image* col;
};

int colors[] = {
DBlack,
DRed,
DGreen,
DBlue,
DCyan,
DMagenta,
DDarkyellow,
DDarkgreen,
DPalegreen,
DMedgreen,
DDarkblue,
DPalebluegreen,
DPaleblue,
DBluegreen,
DGreygreen,
DPalegreygreen,
DYellowgreen,
DMedblue,
DGreyblue,
DPalegreyblue,
DPurpleblue
};

Particle A[N], B[N];
Particle *prev = A, *cur = B;

void
reset(void)
{
int j, grid = sqrt(N)+0.5;
Particle *p;
draw(screen, screen->r, display->white, 0, ZP);
for(j=0;j<N;j++) {
p = prev+j;
p->x = 2*(j%grid)+frand()/2;
p->y = 2*(j/grid)+frand()/2;
p->vx = 1.*v0*frand();
p->vy = 1.*v0*frand();
p->prevx = p->x - p->vx * dt;
p->prevy = p->y - p->vy * dt;
p->col = allocimage(display, Rect(0,0,1,1), RGB24, 1, colors[rand()%(sizeof(colors)/sizeof(int))]);
if(!p->col) sysfatal("allocimage");
}
}

void
main()
{
srand(time(0));
initdraw(0, 0, "Molecular Dynamics");
einit(Emouse | Ekeyboard);

int j;
Particle *p, *q;
double dx, dy, R, F;

reset();

while(1) {
memset(cur, 0, sizeof(Particle) * N);
for(p=prev;p<prev+N;p++) {
for(q=prev;q<p;q++) {
dx = p->x - q->x;
dy = p->y - q->y;
R = dx*dx + dy*dy;
if(R >= 9) continue;
R = 1/sqrt(R);
double R2, R4, R6, R12;
R2 = R * R;
R4 = R2 * R2;
R6 = R4 * R2;
R12 = R6 * R6;
F = 24*(2*R12 - R6);
dx *= F;
dy *= F;
(p-prev+cur)->ax += dx;
(p-prev+cur)->ay += dy;
(q-prev+cur)->ax -= dx;
(q-prev+cur)->ay -= dy;
}
}
for(j=0;j<N;j++) {
int x, y;
p = prev+j;
q = cur+j;
q->x = 2*p->x - p->prevx + q->ax * dt*dt;
q->y = 2*p->y - p->prevy + q->ay * dt*dt;
q->vx = (q->x - p->prevx) / (2*dt);
q->vy = (q->y - p->prevy) / (2*dt);
q->prevx = p->x;
q->prevy = p->y;
q->col = p->col;
x = (screen->r.max.x - screen->r.min.x) * (q->x - xmin) / (xmax - xmin) + screen->r.min.x;
y = (screen->r.max.y - screen->r.min.y) * (q->y - ymin) / (ymax - ymin) + screen->r.min.y;
draw(screen, Rect(x, y, x+1, y+1), p->col, 0, ZP);
}

Particle* tmp = prev;
prev = cur;
cur = tmp;
flushimage(display, 0);

if(ecankbd()) {
switch(ekbd()) {
case 'q': exits(0); break;
case 'r': reset(); break;
case 'f': draw(screen, screen->r, display->white, 0, ZP); break;
}
}
}
}

void
eresized(int new)
{
if(new) getwindow(display, Refnone);
}

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