Page 5 of 8~104 min topic

Prediction: your first ML idea

Debug threshold outside 0..1 in the threshold prediction game

Page 5 reproduces and repairs the characteristic failure of the threshold tuner on five labeled scores: threshold outside 0..1, or reporting accuracy without TP/FP/TN/FN.

~13 min this pageDebugging

1Learn the idea

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Reproduce before you repair

Do not start with a speculative fix for the threshold prediction game. Force the failure on purpose, save the before output, then change one cause at a time. Retries are allowed only for transient conditions—not for bad input that will fail forever on prediction-game.

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Force the failure

try:
    thr=1.5
    if not 0<=thr<=1: raise ValueError('threshold out of range')
except ValueError as e:
    print(e)

Expected evidence: threshold out of range. If you cannot reproduce on demand, you do not yet control the failure mode for prediction-game.

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Repair with a reviewable diff

After repair, rerun the exact reproduction command. Keep the failing fixture as a regression seed for the observability page. For the threshold tuner on five labeled scores, remember the claim you are restoring: for a chosen threshold, accuracy and confusion counts are exact on the fixture.

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Lab notebook: reproduce on command

Store a one-command reproduction for: threshold outside 0..1, or reporting accuracy without TP/FP/TN/FN. The command should use 5 (truth, score) pairs or a minimal mutant of it. Paste the failing output into notes/failure-before.txt (or your shell scrollback as copied text). After the fix, paste notes/failure-after.txt and keep both.

Retries belong only on transient faults. If the failure is bad input, a bad allowlist, or a logic bug in the threshold prediction game, retrying will amplify cost without repairing trust around choose a cutoff that balances errors without claiming generalization from five rows.

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Worked judgment

Classify the failure as prevent, detect, contain, or recover—using this lab’s language, not a generic poster. For prediction-game, the first fix should usually be detect+prevent at the boundary, because threshold outside 0..1, or reporting accuracy without TP/FP/TN/FN is cheaper to stop early than to explain in production prose.

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Why this stage matters for the threshold prediction game

At the debugging stage for prediction-game, the job is narrower than finishing a product demo. You are creating one progressive evidence piece about 5 (truth, score) pairs that later pages inherit without redefining success. Keep that fixture small enough to inspect by hand, keep outputs copy-pasteable as text, and refuse to narrate this baseline as if it were a production SLA: confusion counts computed by hand at threshold 0.5.

For this page specifically, success looks like before/after evidence for the characteristic failure while still centering the user decision to choose a cutoff that balances errors without claiming generalization from five rows. If you cannot point to a file, command, or assertion that proves that for the threshold prediction game, stay on this page instead of advancing.

Confusion matrix glossary

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Before you start

Why this matters

Describe the smallest fixture that triggers threshold outside 0..1. Predict the first visible symptom (exception, wrong label, silent empty success). You will compare that prediction with the reproduction below.

Check your understanding

Page assessment

Answer from memory. Completion is saved from this evidence, not from opening the next page.

1. Can you reproduce the failure with a one-command fixture?
2. Did you avoid retrying non-transient bad input?
3. Is before/after evidence saved as text (not only a screenshot)?
4. Does the repair restore the metric path toward: confusion matrix sums to 5?

All responses are required.