Draw a distribution. Then hunt it.

Click the map to drop a mode, drag it to move it, and shape it with the sliders. A live Markov chain samples whatever you build — it is never told where the modes are. The histograms on the top and right edges are what the chain believes; the pale outlines are the truth. Make them disagree.

Click empty space to add a mode · drag a mode to move it · click a mode to select and reshape it · everything updates while the chain runs.

Sampler

Step size 2.51

HMC steps L 15

Speed 6

Presets

Mixture components 0

No modes yet.
Click anywhere on the map to place one.

Width σ_a 0.80

Height σ_b 0.80

Rotation 0°

Weight 1.00

Target & chain random-walk Metropolis

accepted samples walker true density & marginals the chain's histograms Dashed circles mark each component's 1σ ellipse — the shape you drew, not anything the chain knows.

Iterations

Acceptance

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ESS · x

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ESS · y

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Mass explored

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Verdict

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Traces x in teal, y in amber — the last 1 200 iterations

A trace that parks on one level for hundreds of steps is a chain stuck in a single mode. Widen the step size, or switch sampler, and watch the traces start jumping between levels.