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[diderot] Annotation of /trunk/test/iso2d.diderot
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Annotation of /trunk/test/iso2d.diderot

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1 : jhr 1115 // iso2d
2 :     //
3 :     // Demo of finding isocontours via Newton-Raphson method.
4 :     // Initializes positions on a grid, and each update applies one
5 :     // step of Newton-Raphson.
6 :     //
7 :     // Process output with:
8 :     // unu jhisto -i mip.txt -b 512 512 -min 0 0 -max 1 1 | unu 2op neq - 0 | unu quantize -b 8 -o iso2d.png
9 :    
10 :     int gridSize = 300;
11 :     field#1(2)[] F = load("../data/ddro-80.nrrd") ⊛ ctmr;
12 :     int stepsMax = 10;
13 :     real epsilon = 0.0001;
14 :    
15 :     strand sample (int ui, int vi) {
16 :     output vec2 pos = [lerp(0.0, 1.0, -0.5, real(ui), real(gridSize)-0.5),
17 :     lerp(0.0, 1.0, -0.5, real(vi), real(gridSize)-0.5)];
18 :     // set the isvalue to 50, 30, or 10, depending on whichever we're closest to
19 :     real isoval = 50.0 if F(pos) >= 40.0 else 30.0 if F(pos) >= 20.0 else 10.0;
20 :     int steps = 0;
21 :     update {
22 :     // We bail if we're no longer inside or taken too many steps.
23 :     // We tag this strand result as garbage by setting it to a
24 :     // non-finite position; these will be filtered later.
25 :     // This is really what "die" is for, though (see below).
26 :     if (!inside(pos, F) || steps > stepsMax) {
27 : jhr 1131 die;
28 : jhr 1115 }
29 :     vec2 grad = ∇F(pos);
30 :     real gmsq = grad • grad;
31 :     // If |∇F|=0 we can't compute update; we have to bail
32 :     if (gmsq == 0.0) {
33 : jhr 1131 die;
34 : jhr 1115 }
35 :     // delta = Newton-Raphson step
36 :     vec2 delta = -(F(pos) - isoval)*grad/gmsq;
37 :     // We've converged if the update is small enough
38 :     if (|delta| < epsilon) {
39 :     stabilize;
40 :     }
41 :     pos = pos + delta;
42 :     steps = steps + 1;
43 :     }
44 :     }
45 :    
46 :     initially { sample(ui, vi) | vi in 0..(gridSize-1), ui in 0..(gridSize-1) };

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