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[diderot] View of /examples/iso2d-spatial/iso2d-glk2.diderot
 [diderot] / examples / iso2d-spatial / iso2d-glk2.diderot

# View of /examples/iso2d-spatial/iso2d-glk2.diderot

Revision 2985 - (download) (annotate)
Sat Mar 7 00:22:32 2015 UTC (4 years, 4 months ago) by glk
File size: 4185 byte(s)
`more comments, another bug`
```int gridSize = 10;
real isoval = 1;
field#1(2)[] F = bspln3 ⊛ image("data/hex.nrrd");
input int newtonIterMax = 50;
input real stepScale = 1.0;
real epsilon = 0.0001;
//////////////// Global Variables for Spacing Particles //////////////////////
input real rr = 0.4;      // actual particle radius
real stepMax = rr/2;
real evariance = ∞;
real hhInit = 10.0;  // initial integration step size; can err too big, will be trimmed down during iterations
int iterSpacing = 1;             // which iteration we're on
input int forceIterMax = 20;
/////////////////////////////////////////////////////////////////////////////

strand Particle (int ID, vec2 pos0) {
vec2 pos = [pos0[0] - pos0[1]/gridSize, pos0[1] + pos0[0]/gridSize];
output vec2 outPos = [0,0];

bool foundContour = false;
int forceIter = 1;
int newtonIter = 0;
real energy = 0;     // HEY: can do convergence test based on variance of energies
vec2 force = [0,0];   // or can test convergence based on sum of |force|

vec2 posOld = pos;
real hh = hhInit;

stabilize {
outPos = pos;
}

update {
if (!foundContour) {
// We bail if we're no longer inside or taken too many steps.
if (!inside(pos, F) || newtonIter > newtonIterMax) {
die;
}
if (|∇F(pos)| == 0.0) {  // can't compute step if |∇F|, so have to bail
die;
}
vec2 delta = -((F(pos) - isoval)/|∇F(pos)|)*normalize(∇F(pos));  // Newton-Raphson step
if (|delta| < epsilon) {    // we've converged if step is small enough
foundContour = true;
} else {
pos += delta;
newtonIter += 1;
}
} else { // if (!foundContour)
if (forceIter > forceIterMax) {
stabilize;
}
energy = 0;
force = [0,0];
foreach (Particle p_j in sphere(rr)) {
if (p_j.foundContour) {
vec2 r_ij = (pos - p_j.pos)/rr;
if (|r_ij| < 1) {
energy += (1 - |r_ij|)^4;
force += - (-4*(1 - |r_ij|)^3) * normalize(r_ij);
}
}
}
force /= rr;     // smaller particles make larger forces
// update position based on force
posOld = pos;
if (energy > 0.0) {  // we have neighbors
tensor[2,2] pten = identity[2] - normalize(∇F(pos))⊗normalize(∇F(pos));
force = pten•force;  // project force onto tangent surface
vec2 step = hh*force;
if (|step| > stepMax) {
// decrease hh by factor by which step was too big
hh *= stepMax/|step|;
// and find smaller step
step = hh*force;
}
// take step and re-find implicit surface
pos += step;
pos += -((F(pos) - isoval)/|∇F(pos)|)*normalize(∇F(pos));  // Newton-Raphson step
pos += -((F(pos) - isoval)/|∇F(pos)|)*normalize(∇F(pos));  // Newton-Raphson step
real newenergy = 0;
foreach (Particle p_j in sphere(rr)) {
if (p_j.foundContour) {
vec2 r_ij = (pos - p_j.pos)/rr;
if (|r_ij| < 1) {
newenergy += (1 - |r_ij|)^4;
}
}
}
if (newenergy > energy) {
// bad step: energy went up;
// try again next time with smaller step
hh *= 0.5;
pos = posOld;
}
} // if (energy > 0.0)
forceIter +=1;
} // if (!foundContour)
}
}
global{
real energyMean = mean{P.energy | P in Particle.all};
evariance = mean{ (P.energy - energyMean) * (P.energy - energyMean) | P in Particle.all};
}

initially { Particle(ui + gridSize*vi,
[lerp(-1.5, 1.5, -0.5, real(ui), real(gridSize)-0.5),
lerp(-1.5, 1.5, -0.5, real(vi), real(gridSize)-0.5)])
| vi in 0..(gridSize-1), ui in 0..(gridSize-1) };
```

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