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Generalized Bayes loss updates and temperature calibration — Examples
1 · Prerequisites
- Absolute and Conditional Convergence; Rearrangement; Products
- Binary Operations, Monoids, Groups and Subgroups
- Compactness in Metric Spaces
- Complete Metrizability, Čech-Completeness, and Baire Category
- Completeness, Completion, and Uniform Continuity
- Confidence Sets and Inversion
- Construction of the Natural Numbers
- Construction of the Real Numbers via Cauchy Sequences
- Construction of the Real Numbers via Dedekind Cuts
- Continuity, IVT, EVT, and Uniform Continuity
- Countability and Uncountability
- Countability Axioms and Cardinal Functions
- Dirichlet-process priors and finite-partition updates
- Finite Counting, Factorials and Binomial Coefficients
- Finite Probability Spaces and Random Variables
- Foundations of the Real Numbers for Analysis
- Generalized Bayes loss updates and temperature
- Infinite Product Measures and Kolmogorov Extension
- Limits of Real Functions
- limsup, liminf, and Subsequential Limits
- Measurable Functions and Simple Approximation
- Measures and Their Basic Properties
- Metric Spaces
- Monotone Functions, Discontinuities, and Continuity Sets
- Monotone Sequences, Bolzano-Weierstrass, and Cauchy Completeness
- Order, Zorn's Lemma, and the Axiom of Choice
- Power Series and Real-Analytic Functions
- Probability Spaces Random Variables and Expectation
- Properties of the Integral and the Working FTC
- Relations, Functions, and Quotients
- Roots, Rational Powers, and Classical Inequalities
- Sequences and Limits
- Sequences and Series of Functions; Uniform Convergence
- Series: Convergence and the Nonnegative Tests
- Sigma Algebras and Borel Sets
- Statistical Experiments, Models and Identifiability
- Suprema and Infima
- The Derivative and the Mean Value Theorems
- The Exponential Function
- The Lebesgue Integral and the Convergence Theorems
- The Logarithm and General Powers
- The Riemann Integral: Definition and Integrability
- The ZFC Axioms and the Basic Set Constructions
- Topological Spaces and Continuity
- Topology of ℝ
- Vector Spaces, Linear Subspaces, Span and Direct Sums
2 · Summary
Finite and countable constructions make the normalizer and temperature conditions explicit. The unit-temperature likelihood example is a finite Bayesian model calculation; rescaling the loss shows the equivalent change in effective temperature. A separate dyadic prior has an infinite normalizer, and a two-state experiment produces a posterior credible set with zero frequentist coverage. Each calculation states its prior, loss and temperature locally; the coverage and likelihood examples also specify their finite sampling experiments. None asserts a general coverage theorem.
3 · Logical flowchart
4 · Definitions, theorems and proofs
None yet.
5 · Examples, counterexamples and false statements
A measurable loss can have an infinite normalizer
Example
Let with its power-set sigma-algebra, and put for . Define the prior where is the Dirac measure at . The geometric-series formula gives , so is a probability measure. Define the real-valued loss . At temperature , every unnormalized atom has mass , and the normalizer is infinite; therefore the loss update is not defined.
Facts & Assumptions
Given: The von Neumann natural numbers , their power-set sigma-algebra, weights , and Dirac measures .
Generalized Bayes loss update and temperature: at fixed , must be finite and positive for the update to be defined.
A countable discrete measurable space is standard Borel: every nonempty at-most-countable set with its power-set sigma-algebra is standard Borel.
Finite, countably infinite, countable, uncountable: a set equinumerous with is at-most-countable.
The natural numbers (von Neumann): and is closed under successor.
Nonnegative scalar multiples and countable weighted sums of measures are measures: a countable nonnegative weighted sum of measures on one measurable space is a measure.
The Dirac set function at a point: when and is zero otherwise.
A Dirac set function is a probability measure: each is a probability measure.
Probability measures and probability spaces: a probability measure has total mass one.
The principle of mathematical induction: a property holding at zero and preserved by successor holds for all natural numbers.
Integer powers : and for natural .
For , , and for the series diverges: for , .
The natural logarithm as the inverse of the exponential function: is inverse to on .
Nonnegative simple measurable functions: a finite nonnegative linear combination of indicators of measurable sets is a nonnegative simple measurable function.
The nonnegative Lebesgue integral: the nonnegative integral is the supremum of the integrals of nonnegative simple minorants, with values in .
The integral of a nonnegative simple function: the integral of a simple function represented on disjoint measurable sets is the sum of its coefficient times the measure of each set.
The nonnegative integral agrees with the simple integral on simple functions: the nonnegative integral of a simple function equals its simple integral.
The Cauchy-sequence reals have the least-upper-bound property: is a complete ordered field.
Every complete ordered field is Archimedean: in a complete ordered field, for every there is a natural with .
Absolute value in an ordered field: if , then .
Ordered field: products of positive reals are positive.
Laws of finite sums and finite products: finite sums scale by a real constant, .
Series, partial sums, convergence and the sum, divergence, and the tail series: a convergent series sums to the limit of its finite partial sums.
Algebra of limits: sums, scalar multiples, products and quotients: scaling a convergent sequence by a fixed real constant scales its limit by that constant.
A series of nonnegative terms converges iff its partial sums are bounded, and then the sum is their supremum: for nonnegative terms, the usual convergent series sum is the supremum of its finite partial sums.
Series in the nonnegative extended real line: the nonnegative extended sum is the supremum of its finite partial sums.
Nonnegative scalar multiples and countable weighted sums of measures: the countable weighted sum is evaluated pointwise by the nonnegative extended sum of its weighted measures.
Verification
The identity map shows is equinumerous with itself, hence at-most-countable by [F3]; [F4] makes it nonempty. Therefore [F2] shows is standard Borel.
Put . Ordered-field arithmetic gives , so [F21] gives . The powers are positive: by [F10] and [F23], and if , then by [F10] and [F22]. Induction [F9] gives for every .
By [F11], . For every , recursion [F10] and finite-sum scaling [F24] give The partial sums of converge to by [F11] and [F25]; therefore [F26] gives . By [F27] and [F28], this usual series sum is also the nonnegative extended sum of the coefficients used in the weighted measure.
Since , is finite. Every inverse image of a Borel subset of is a subset of , hence is in ; therefore is measurable. By [F12]–[F13], , so the normalizer is .
By [F5] and [F7], is a measure. Its total mass is by [F6], [F28], [F29], and step 2.1, so [F8] makes a probability. For each , [F6] gives .
For each , set It is a nonnegative simple function by [F14], and : there is equality at , and for the left side is zero while by [F13]. By [F16]–[F17] and step 3.1, Thus [F18] yields for every .
If were finite, [F19]–[F20] would give , , with . Step 4.1 gives , a contradiction. Since [F15] places in , it follows that . The finite-positive condition in [F1] therefore fails, so no generalized Bayes update is defined.
A generalized Bayes credible set can have zero coverage
Statement refuted
A positive temperature and a proper generalized Bayes loss update alone guarantee that every posterior -credible set has frequentist coverage at least under the sampling experiment.
Facts & Assumptions
Given: The finite parameter space , singleton observation space , prior , sampling laws , and the displayed loss at .
A countable discrete measurable space is standard Borel: a nonempty at-most-countable set with its power-set sigma-algebra is standard Borel.
Probability measures and probability spaces: a probability measure has total mass one.
The Dirac set function at a point: if and is zero otherwise.
A Dirac set function is a probability measure: each Dirac set function is a probability measure.
Statistical experiments: an experiment consists of a sample measurable space, parameter set and a probability law on the sample space for each parameter.
Generalized Bayes loss update and temperature: if , the update is the normalized measure with that density.
A finite-normalizer loss update is a probability measure: each update with a finite positive normalizer is a probability measure.
The exponential is positive and satisfies : and for real .
The exponential function is strictly increasing: the exponential is strictly increasing on .
Confidence sets and coverage: a confidence-set procedure maps data to parameter subsets with measurable membership sections; coverage at is the sampling probability that its set contains .
Counterexample
Let and , each with its power-set sigma-algebra. Use prior , , and sampling laws . At the sole observation , let and , with temperature . The singleton data-to-set rule is called -credible here when the update satisfies . It has posterior mass greater than , yet its coverage at true parameter is zero.
The parameter and data spaces are nonempty finite sets, so [F1] makes them standard Borel. The prior masses sum to one, hence [F2] makes a probability. [F3]–[F5] show the sampling laws define a statistical experiment. [F6]–[F8] give the normalizer which is finite and positive. By [F7], the resulting update is a probability measure.
Since , [F9] gives . Both are positive by [F8], and Therefore Thus is a posterior credible set of mass greater than .
Verification
Regard as the data-to-set procedure with sole value . Its membership section for parameter is empty, and for parameter is ; both are measurable. The coverage definition [F10] therefore applies, and at true parameter it gives This is below , refuting the proposed universal guarantee.
Rescaling loss changes the effective temperature
Example
Let with its power-set sigma-algebra and prior , for . At a fixed observation , let and with . For every , replacing this loss section by at temperature gives the same update as retaining at temperature . At any two distinct positive temperatures, the updates are different.
Facts & Assumptions
Given: The finite parameter space with its power-set sigma-algebra; an observation ; ; real loss-section values ; and positive temperatures with .
A countable discrete measurable space is standard Borel: every nonempty at-most-countable set with its power-set sigma-algebra is standard Borel.
Probability measures and probability spaces: a probability measure is a measure of total mass one.
Generalized Bayes loss update and temperature: when its normalizer is finite and positive, the update is the measure with density relative to the prior.
A finite-normalizer loss update is a probability measure: each update with a finite positive normalizer is a probability measure.
The exponential function is strictly increasing: the exponential is strictly increasing, hence injective, on .
The exponential is positive and satisfies : and for every real .
Verification
The set is nonempty and finite, so [F1] makes its power-set measurable space standard Borel. Since , the masses and are positive and sum to one, so [F2] makes a probability. For every , the two real loss values give positive finite weights and by [F6]; their prior-weighted sum is therefore finite and positive.
By [F3]–[F4], the update has masses Consequently its odds satisfy .
For , the unnormalized weight after replacing by at temperature is . These are exactly the unnormalized masses for . The two updates have the same finite positive normalizer by step 1.1, so their values on both singletons, and hence on every subset of , agree.
Because and , the real numbers and differ. Injectivity in [F5] makes their exponentials different. Multiplication by the fixed positive factor preserves that difference, so step 2.1 gives distinct odds. On a two-point probability space the odds determine both singleton masses; therefore .
The unit-temperature likelihood update is ordinary Bayes in a finite model
Example
Let have prior masses and . Let the observation space be and define sampling laws by , , , and . These finite spaces with power-set sigma-algebras are standard Borel, and the displayed laws define a statistical experiment. Take for every . For observed at , the unnormalized masses are and , so the update is . The same values follow by conditioning the joint prior-sampling law on .
Facts & Assumptions
Given: The parameter and observation spaces with power-set sigma-algebras, prior , and the four displayed sampling probabilities.
A countable discrete measurable space is standard Borel: a nonempty at-most-countable set with its power-set sigma-algebra is standard Borel.
Probability measures and probability spaces: a probability measure has total mass one.
Statistical experiments: a statistical experiment consists of a sample measurable space, a parameter set, and a probability law on the sample space for each parameter.
Generalized Bayes loss update and temperature: at the update weights are proportional to and are normalized by their integral against the prior.
A finite-normalizer loss update is a probability measure: a finite-positive-normalizer update is a probability measure.
The natural logarithm as the inverse of the exponential function: is the inverse of on .
Conditional probability for : in a finite probability space, when .
Verification
Both parameter and sample spaces are nonempty finite sets, so [F1] makes them standard Borel. The prior masses are nonnegative and sum to one; each pair of sampling probabilities is nonnegative and sums to one. By [F2] these are probability measures, and [F3] therefore gives the stated finite statistical experiment.
All four likelihoods are positive, so [F6] makes real-valued on . Each parameter section is measurable because the parameter sigma-algebra is the power set, satisfying the loss hypotheses of [F4] for every . At , the inverse relation in [F6] gives . Hence the unnormalized weights are and their normalizer is , finite and positive.
By [F4]–[F5], the update is a probability measure with .
Define the joint masses by . The four masses are at , respectively; they sum to one, and . Applying [F7] to each parameter singleton gives Thus the loss update equals the ordinary finite-model posterior at .
Sources
- P. G. Bissiri, C. C. Holmes, and S. G. Walker, A general framework for updating belief distributions, JRSS B 78(5), 2016
- L. Perrotta, Practical Calibration of the Temperature Parameter in Gibbs Posteriors, arXiv:2004.10522, 2020
- J. Knoblauch, J. Jewson, and T. Damoulas, An Optimization-centric View on Bayes’ Rule: Reviewing and Generalizing Variational Inference, JMLR 23(132), 2022