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[diderot] View of /tests/lamont-tests/unit-circle1.diderot
 [diderot] / tests / lamont-tests / unit-circle1.diderot

# View of /tests/lamont-tests/unit-circle1.diderot

Tue Sep 27 20:54:47 2016 UTC (2 years, 8 months ago) by glk
File size: 2972 byte(s)
`initial result of svn export --username anonsvn --password=anonsvn https://svn.smlnj-gforge.cs.uchicago.edu/svn/diderot/branches/vis15/src/tests/`
```// unit-circle
//
// Demo of distributing particles on the unit circle
//
vec2{} initPosns = load("-");
int numOfParticles = length(initPosns);
input int iterMax = 500;  // maximum number of steps to run
input real rad = 0.2;       // particle radius
real hh0 = 1000; // initial step size, can be big
int iter = 1;             // which iteration we're on
real stepMax = 2*rad;  // limit on distance to travel per iter

// inter-particle energy, and its derivative
function real  φ(real r) = (1 - r)^4;
function real φ'(real r) = -4*(1 - r)^3;
//function real  φ(real r)  =  (1/r)*(1-r)^3;
//function real φ'(real r) = 3 - 1/(r^2) - 2*r;
function real enr(vec2 x) = φ(|x|/rad);
function vec2 frc(vec2 x) = φ'(|x|/rad) * (1/rad) * x/|x|; // chain rule

strand Particle (int ii, vec2 pos0) {
vec2 pos = pos0/|pos0|;
real hh = hh0;
output vec2 outPos = pos;
vec2 dpos = [0,0];
int id = ii;
real energyLast = ii;     // HEY: can do convergence test based on variance of energies
vec2 force = [0,0];   // or can test convergence based on sum of |force|
update {
// compute energy and forces on us
if (!( pos[0] <= 0 || pos[0] > 0 )) {
print(ii"HEY pos = ", pos, "\n");
}
energyLast = 0;
force = [0,0];
int ncount = 0;
foreach (Particle p_j in sphere(rad)) {
ncount += 1;
vec2 r_ij = p_j.pos - pos;
energyLast += enr(r_ij);
force += frc(r_ij);
}
vec2 norm = normalize(pos);
if (ncount < 2) {
if (iter % 3 == 0) {
vec2 npos = pos + 0.2*rad*[norm[1],-norm[0]];
new Particle(0, npos);
}
}
// update position based on force
force = (identity[2] - norm⊗norm)•force;  // project force onto tangent surface
dpos = hh*force;
if (|dpos| > stepMax) {
// decrease hh by factor by which step was too big
hh *= stepMax/|dpos|;
// and find smaller step
dpos = hh*force; // == stepMax*normalize(force);
}
vec2 posLast = pos;
// take step and re-apply constraint
pos = normalize(pos + dpos);
real energy = 0;
foreach (Particle p_j in sphere(rad)) {
energy += enr(p_j.pos - pos);
}
if (energy - energyLast > 0.5*(pos - posLast)•(-force)) {
hh *= 0.5; // backtrack
pos = posLast;
} else {
hh *= 1.1;
}
outPos = pos;
}
}

global {
/*
real mvmt = mean { |P.dpos|/rad | P in Particle.all};
if (mvmt < 0.0001) {
print("stabilized at iter ", iter, "\n");
stabilize;
}
*/
iter+=1;
if (iter > iterMax)  {
print("numActive() = ", numActive(), "\n");
stabilize; // HEY really want "die" here: didn't converge
}
//  real var = variance{P.energy | P in Particle.all};
//  real var = sum{(avg-P.energy)^2 | P in Particle.all};
}

initially {Particle(ii, initPosns[ii])
| ii in 1 .. numOfParticles };
```

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