Annotation of /branches/vis12/bugs/open/bug027.diderot

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1 :	glk	2334	// bug: won't work: field#1(2)[] F = bspln3 ⊛ image("../data/ddro.nrrd") - isoval;
2 :			// field#2(2)[] F = bspln3 ⊛ image("../data/ddro.nrrd") - isoval;
3 :
4 :
5 :			/*
6 :			$DDRO_HOME/branches/vis12/bin/diderotc --exec bug027.diderot \
7 :			&& ./bug027 \
8 :			&& unu jhisto -i x.nrrd -b 800 800 -min 0 0 -max 1 1 \
9 :			| unu 2op neq - 0 \
10 :			| unu quantize -b 8 -o bug027.png
11 :			*/
12 :
13 :			input real isoval = 0.5;
14 :			/* BUG: it looks like the type promotion from field#2 to field#1
15 :			doesn't work with subtracting a constant
16 :			error converting OffsetField
17 :			uncaught exception Fail [Fail: bogus operator OffsetField]
18 :			raised at common/phase-timer.sml:76.50-76.52
19 :			raised at common/phase-timer.sml:76.50-76.52
20 :			raised at high-to-mid/high-to-mid.sml:297.85-297.87
21 :			raised at high-to-mid/high-to-mid.sml:294.32-294.78
22 :			*/
23 :			field#1(2)[] F = bspln3 ⊛ image("../data/ddro.nrrd") - isoval;
24 :
25 :			int grid = 150;
26 :			int stepsMax = 10;
27 :			real epsilon = 0.000001;
28 :
29 :			strand RootFind(vec2 x0) {
30 :			output vec2 x = x0;
31 :			int steps = 0;
32 :			update {
33 :			// Stop if we're no longer inside or taken too many steps.
34 :			if (!inside(x, F) || steps > stepsMax)
35 :			die;
36 :			vec2 grad = ∇F(x);
37 :			// subsequent expressions are undefined if |∇F| is zero
38 :			if (|grad| == 0.0)
39 :			die;
40 :			// the Newton-Raphson step
41 :			vec2 delta = normalize(grad) * F(x)/|grad|;
42 :			// we've converged if the change is small enough
43 :			if (|delta| < epsilon)
44 :			stabilize;
45 :			x -= delta;
46 :			steps += 1;
47 :			}
48 :			}
49 :
50 :			initially { RootFind([lerp(0, 1, -0.5, ui, grid-0.5),
51 :			lerp(0, 1, -0.5, vi, grid-0.5)])
52 :			| vi in 0..(grid-1), ui in 0..(grid-1) };
53 :
54 :			/*
55 :			different in 3D:
56 :			vec2 -> vec3
57 :			field#1(2)[] F -> field#1(3)[] F
58 :			initially over 3D grid
59 :			*/

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