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The score-matching integration-by-parts identity
Statement
Assume the Axiom of Countable Choice used by the library's Lebesgue-measure and weak-derivative representative interfaces. Let , let be Lebesgue measure on , and let be a continuously differentiable probability density, so . Write which is a probability measure, and let for integrable . Define the data score by when and set when . For an energy model relative to with , assume and define its model score field by . Assume each component of is locally integrable and has locally integrable weak first derivatives: for each , a locally integrable representative satisfies Here denotes the smooth compactly supported test functions. The weak derivatives are unique up to Lebesgue-null sets, and define ; the integrals below do not depend on the chosen representatives. The convention is that the first derivative exists everywhere and is continuous. For each admissible , assume Then the score-matching objective satisfies where is independent of . No pointwise boundary limit at infinity is assumed.
Statement references
Aapo Hyvärinen, Theorem 1 and Appendix A of the full JMLR paper states the score-matching identity under a pointwise boundary condition.
Kevin P. Murphy, Chapter 24, Sections 24.1–24.3.4 defines energy models, the model score and score matching.
Facts & Assumptions
Given: The hypotheses in the Statement, including Countable Choice for the library Lebesgue measure interface and the three stated finite -integrability conditions.
is a nonnegative probability density; for each admissible parameter, , its score field is locally integrable with locally integrable weak first derivatives, and the score and divergence have the stated finite -moments.
The Axiom of Countable Choice (): every countable family of nonempty sets has a choice function; it is used through [F3], [F8], [F10], [F17], and [F19].
Energy-based density and partition function: for , the model density is , and is independent of .
The measure with density relative to : for a nonnegative measurable density , is the measure .
Assuming countable choice, is a sigma-algebra containing every elementary set and is a complete measure extending elementary volume: under Countable Choice, is a complete measure on the Lebesgue sigma-algebra of .
Dominated convergence: almost-everywhere convergence under one integrable majorant implies convergence of the corresponding integrals.
Probability measures and probability spaces: a measure of total mass one is a probability measure.
Continuously differentiable maps, local inverses, and local diffeomorphisms: a map on an open Euclidean set is when it is differentiable everywhere and its derivative entries are continuous.
Weak derivative of a locally integrable function: is a weak derivative exactly when its signed test-function identity holds for every smooth compactly supported test function.
Uniqueness of a weak derivative as an almost-everywhere class: under Countable Choice, any two locally integrable representatives satisfying the same weak-derivative identity agree almost everywhere.
A continuous map has Borel preimages of Borel sets: a continuous map has Borel preimages of Borel sets.
Assuming countable choice, every Borel subset of is Lebesgue measurable: under Countable Choice, Borel subsets of are Lebesgue measurable.
A smooth bump between concentric Euclidean balls: for , a smooth function can equal on and have support contained in .
A continuous real-valued function on a nonempty compact metric space is bounded and attains a greatest and a least value: continuous real functions on nonempty compact metric spaces are bounded.
Chain sum product and composition rules for Banach derivatives: total derivatives obey the bounded-bilinear product rule.
Monotonicity and nonnegative homogeneity of the nonnegative integral: the nonnegative integral is monotone and positively homogeneous.
A C^1 diffeomorphism satisfies the change-of-variables formula for nonnegative Lebesgue measurable functions: a diffeomorphism transforms nonnegative Lebesgue integrals by its absolute Jacobian determinant.
The mollifier family generated by a unit-mass smooth bump: a unit-mass smooth compactly supported function generates the scaled family .
Convolution with a mollifier is smooth, and derivatives pass under the integral sign: convolution of a locally integrable function with a smooth compactly supported mollifier is smooth.
Differentiation under the integral sign: an integrable parameter-independent majorant permits differentiation under the integral sign.
Fermat's theorem: an interior differentiable local extremum has zero gradient: a differentiable function at an interior local extremum has zero gradient.
The Jacobian matrix of partial derivatives and the gradient in the scalar-valued case: the gradient coordinates of a scalar-valued function are its coordinate partial derivatives.
Total differentiability gives a local increment bound and therefore continuity: total differentiability implies continuity.
Chain sum product and composition rules for Banach derivatives: total derivatives obey the chain rule.
Proof
By [F1], the admissible model has density , with independent of . Since is , [F6, F23] make it continuous; [F9, F10] then make it Lebesgue measurable, so [F2] makes a measure, and [F5] makes it a probability measure. The local increment bound [F23] gives, at each , constants with for ; taking shows , so is open. On , [F6, F15, F24] make continuous. For each open , its score preimage is the union of the relative-open preimage in and when ; hence the zero extension is Borel and Lebesgue measurable by [F10]. By [F8], weak-derivative representatives agree off a Lebesgue-null set; [F2] makes every such set -null, so the divergence integral is representative-independent. Choose from [F11] with and . By [F9, F10], this continuous bump is Lebesgue measurable. Its gradient vanishes outside ; [F12, F13] make finite. The box lies in , since its points have norm at most , while and . Thus [F3, F16] give . Set ; positive homogeneity [F16] gives it unit mass. Let be its scaled family from [F18]; [F18] gives support in and [F17] gives unit mass. For , define . Then on , vanishes outside , and [F24] gives .
Fix and put . The product rule [F14] makes a nonnegative function supported in . By [F12, F13], and its first derivatives are bounded there; the ball lies in a finite-volume box by [F3], so is locally integrable. The convolution is smooth by [F19] and supported in for , since and . By [F17], applied to the nonnegative convolution integrand, . For each coordinate , [F24] gives the parameter derivative of . Its sections are integrable because is bounded and the kernel has mass one; its derivative is measurable and bounded by , an integrable majorant. Thus [F20] gives . The unit mass and shrinking support give, for each , , with the same estimate for each first derivative. Since and are bounded by [F12, F13], the weak-identity integrands are dominated on this common compact support by constants times and . Local integrability and [F4] pass the identities from to . Summing over and expanding with [F14] yields .
On , [F15, F24] give . At any point where , nonnegativity makes it an interior local minimum, so [F21, F22] give there too. Thus everywhere. Componentwise and imply and . Also , so the cutoff term from step 1.1 is bounded in absolute value by .
Let for integers . Then pointwise and . The first integrand in step 2.1 is dominated by and the third by , both integrable by step 2.2. Applying [F4] to both terms and using the vanishing cutoff term from step 2.2 gives .
Expanding the square gives . Since by step 2.2, step 3.1 turns the last term into ; the remaining data-score term is , independent of .
Remarks
The cutoff and integration-by-parts argument is choice-free once the Lebesgue measure and weak-derivative classes are available. Countable Choice is used for those two interfaces; no full Axiom of Choice is used. The cutoff estimate supplies the multivariate limit directly and does not rely on pointwise vanishing of at infinity.
Depends on
- Energy-based density and partition function
- The measure with density $f$ relative to $\mu$
- Probability measures and probability spaces
- Lebesgue measurable sets, the family $\mathcal{L}(\mathbb{R}^n)$, and the restricted set function $\lambda_n$
- Assuming countable choice, $\mathcal{L}(\mathbb{R}^n)$ is a sigma-algebra containing every elementary set and $\lambda_n$ is a complete measure extending elementary volume
- The Axiom of Countable Choice ($\mathrm{AC}_\omega$)
- The nonnegative Lebesgue integral
- Integrable real and complex functions, and their integrals
- Dominated convergence
- Continuously differentiable maps, local inverses, and local diffeomorphisms
- Weak derivative of a locally integrable function
- Uniqueness of a weak derivative as an almost-everywhere class
- A continuous map has Borel preimages of Borel sets
- Assuming countable choice, every Borel subset of $\mathbb{R}^n$ is Lebesgue measurable
- A smooth bump between concentric Euclidean balls
- Heine-Borel in $\mathbb{R}^n$: with the Euclidean metric a subset of $\mathbb{R}^n$ is compact if and only if it is closed and bounded, and the proof by bisection uses no choice principle; the same holds on the real line
- A continuous real-valued function on a nonempty compact metric space is bounded and attains a greatest and a least value
- Chain sum product and composition rules for Banach derivatives
- The natural logarithm has derivative 1/x and equals the integral from 1 to x of 1/t
- The Jacobian matrix of partial derivatives and the gradient in the scalar-valued case
- Monotonicity and nonnegative homogeneity of the nonnegative integral
- A C^1 diffeomorphism satisfies the change-of-variables formula for nonnegative Lebesgue measurable functions
- The mollifier family generated by a unit-mass smooth bump
- Convolution with a mollifier is smooth, and derivatives pass under the integral sign
- Differentiation under the integral sign
- Fermat's theorem: an interior differentiable local extremum has zero gradient
- Total differentiability gives a local $O(\|h\|_2)$ increment bound and therefore continuity
Used by
Nothing in the library uses this result yet.
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Sources
- Aapo Hyvärinen, Estimation of Non-Normalized Statistical Models by Score Matching, Theorem 1 and Appendix A (standard reference, not scraped)
- Kevin P. Murphy, Probabilistic Machine Learning: Advanced Topics, Chapter 24, Sections 24.1–24.3.4 (standard reference, not scraped)