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cultmath tests: ThirdNorm ascends from the six strongest starts only (cost of MeasureThird)

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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Meta Vens 2026-10-14 06:43:57 +02:00
commit b8a5a9cc14
1 changed files with 7 additions and 6 deletions
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13
packages/cultmath/tests/CultMath.Tests/NoiseBoundTests.cs
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@ -669,10 +669,11 @@ public sealed class NoiseBoundTests
.Select(v => { var length = Math.Sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]); return new[] { v[0] / length, v[1] / length, v[2] / length }; }).ToArray();
// The operator norm of a symmetric 3-tensor, max over unit u of |T(u, u, u)| (for a symmetric tensor
// that is the injective norm). From each of 26 starts, the shifted power ascent u <- normalise(T(u, u, .)
// +- alpha u), with alpha twice the largest absolute row sum, which makes the iteration monotone in
// the cubic form (Kolda and Mayo's SS-HOPM), the sign chosen as the start's. A local maximum, so a
// lower bound; MeasureThird checks it against a dense direction sweep at its witness.
// that is the injective norm). From the six of 26 starts (axes, edge midpoints, cube corners) with
// the largest |T(u, u, u)|, the shifted power ascent u <- normalise(T(u, u, .) +- alpha u), with alpha
// twice the largest absolute row sum, which makes the iteration monotone in the cubic form (Kolda and
// Mayo's SS-HOPM), the sign chosen as the start's. A local maximum, so a lower bound; MeasureThird
// checks it against a dense direction sweep at its witness.
private static double TensorNorm(double[] t)
{
var alpha = 0.0;
@ -686,11 +687,11 @@ public sealed class NoiseBoundTests
var best = 0.0;
var g = new double[3];
foreach (var start in TensorStarts)
foreach (var start in TensorStarts.OrderByDescending(v => Math.Abs(Cubic(t, v))).Take(6))
{
var u = (double[])start.Clone();
var sign = Cubic(t, u) < 0.0 ? -1.0 : 1.0;
for (var iteration = 0; iteration < 60; iteration++)
for (var iteration = 0; iteration < 40; iteration++)
{
for (var i = 0; i < 3; i++)
{