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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 : jhr 1640 // unu jhisto -i iso2d.txt -b 512 512 -min 0 0 -max 1 1 | unu 2op neq - 0 | unu quantize -b 8 -o iso2d.png
9 : jhr 1115
10 :     int gridSize = 300;
11 : glk 1134 field#1(2)[] F = ctmr ⊛ load("../data/ddro-80.nrrd");
12 : jhr 1115 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 : glk 1134 real isoval = 50.0 if F(pos) >= 40.0
20 :     else 30.0 if F(pos) >= 20.0
21 :     else 10.0;
22 : jhr 1115 int steps = 0;
23 :     update {
24 :     // We bail if we're no longer inside or taken too many steps.
25 :     if (!inside(pos, F) || steps > stepsMax) {
26 : jhr 1131 die;
27 : jhr 1115 }
28 : glk 1329 // GLKs recent changes (revision 1329) were made to make the code
29 :     // a more obvious implementation of Newton-Raphson, and also to create
30 :     // some obvious and not-so-obvious opportunties for optimization
31 : jhr 1115 vec2 grad = ∇F(pos);
32 : glk 1329 if (|grad| == 0.0) { // can't compute step if |∇F|, so have to bail
33 : jhr 1131 die;
34 : jhr 1115 }
35 : glk 1329 vec2 norm = normalize(grad);
36 :     vec2 delta = -((F(pos) - isoval)/|grad|)*norm; // Newton-Raphson step
37 :     if (|delta| < epsilon) { // we've converged if step is small enough
38 : jhr 1115 stabilize;
39 :     }
40 : glk 1329 pos += delta;
41 :     steps += 1;
42 : jhr 1115 }
43 :     }
44 :    
45 :     initially { sample(ui, vi) | vi in 0..(gridSize-1), ui in 0..(gridSize-1) };

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