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fix: persist deep gaussian process layer state and drop the shallow gp clone - #2231

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@ooples ooples commented Sep 20, 2026 •

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What

GaussianProcessBase overrode DeepCopy() with MemberwiseClone(), so every "copy" of a
Gaussian process shared _layers, _X and _y with the original. Clone_ShouldProduceIdenticalPredictions
was comparing a model with itself and could not fail. Removing the override routes the family
through ModelBase.DeepCopy (serialize -> CopyConfiguration -> Deserialize) and exposes two
real defects, both fixed here.

PR #2136 removes the same override as part of its coverage work, which is how its
ModelFamily - Clustering/GP shard went red. That shard needs these two fixes to pass.

Defect 1 - DeepGaussianProcess never serialized what Fit learns

The generated RegisterGeneratedState declares only _X, _y and _yMean. The inducing inputs
and the variational parameters live in the DGPLayer instances, and no member of the model class
holds them, so the state classifier could not place them.

A rebuilt model therefore predicted from the random initialisation DGPLayer.Initialize gives it:
Expected 22.340009820821585, Actual 27.075184895167549. The same path backs SaveModel /
LoadModel, so saving and reloading a DeepGaussianProcess silently discarded all training.

RegisterState now declares the three per-layer matrices positionally and recomputes Kuu after
the restore via DeclareAfterRestore, since Kuu is scratch derived from the inducing inputs and
the kernel. Layer count and widths come from the recorded constructor, so the lists line up.

Defect 2 - the clone path read a parameter count from an unfitted shell

CloneEngine.PrepareParameterTopology and ModelBase.DeepCopy both read a parameter count from
a freshly built configuration shell. A shell whose layout is still FitDeferred throws
ParameterLayoutNotReadyException rather than answer zero -- deliberately, so an unfitted model is
never mistaken for one with no parameters.

There is no fitted topology to bridge in that case, and the caller's Deserialize installs the
fitted state immediately afterwards, so both reads now treat a not-ready layout as "nothing to
bridge" and fall through. This is what GPWithMCMC, StudentTGaussianProcess,
HeteroscedasticGaussianProcess and VariationalGaussianProcess hit once the shallow override
was gone.

Verification

Local, net10.0:

dotnet test --filter "FullyQualifiedName~GaussianProcess"
Passed!  - Failed:     0, Passed:   319, Skipped:     0, Total:   319

Before these fixes the same filter gave Failed: 4 (the four ParameterLayoutNotReadyException
models) plus DeepGaussianProcessTests.Clone_ShouldProduceIdenticalPredictions.

🤖 Generated with Claude Code

Summary by CodeRabbit

  • New Features

    • Deep Gaussian Process models now preserve and restore learned layer state, including inducing inputs and variational parameters.
    • Restored models recalculate required covariance information when inducing inputs are available.
  • Bug Fixes

    • Improved model copying and parameter restoration for models whose parameter layout is determined later.
    • Copy operations now avoid failing when parameter information is temporarily unavailable.
    • Restoration safely handles partial or mismatched saved state without affecting unrelated layers.

…p clone

gaussianprocessbase overrode deepcopy with memberwiseclone, so every "copy" of a
gaussian process shared _layers, _x and _y with the original. clone_shouldproduceidentical
predictions therefore compared a model with itself and could not fail. removing the override
routes the family through modelbase.deepcopy (serialize -> copyconfiguration -> deserialize)
and exposes two real defects.

first, deepgaussianprocess never serialized what fit learns. the generated declarations cover
_x, _y and _ymean; the inducing inputs and the variational parameters live in the layers and
no member of the class holds them, so the classifier could not place them. a rebuilt model
predicted from the random initialisation dgplayer.initialize gives it -- 27.08 against an
expected 22.34 -- which also means savemodel/loadmodel silently discarded all dgp training.
registerstate now declares the three per-layer matrices positionally and recomputes kuu after
the restore, since kuu is scratch derived from the inducing inputs and the kernel.

second, cloneengine.prepareparametertopology and modelbase.deepcopy both read a parameter
count from a fresh configuration shell. a shell whose layout is still fit-deferred throws
parameterlayoutnotreadyexception rather than answer zero, precisely so an unfitted model is
never mistaken for one with no parameters. there is no fitted topology to bridge in that case,
and the caller's deserialize installs the state immediately after, so both reads now treat a
not-ready layout as "nothing to bridge". this is what gpwithmcmc, studenttgaussianprocess,
heteroscedasticgaussianprocess and variationalgaussianprocess hit once the shallow override
was gone.

verified locally: fullyqualifiedname~gaussianprocess passes 319, fails 0 on net10.0.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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  • src/GaussianProcesses/DeepGaussianProcess.cs

Walkthrough

The pull request adds deep Gaussian process layer-state persistence and restoration. It also updates model copying to tolerate fit-deferred parameter layouts and removes the GaussianProcessBase<T> shallow-copy override.

Changes

Model state and copy behavior

Layer / File(s) Summary
Deep Gaussian process state persistence
src/GaussianProcesses/DeepGaussianProcess.cs
DeepGaussianProcess registers per-layer inducing inputs and variational matrices. Restoration uses positional overlap, skips null entries, and recomputes Kuu for initialized layers. DGPLayer exposes internal accessors for these matrices.
Deferred model copy handling
src/Models/ModelBase.cs, src/Models/CloneEngine.cs, src/GaussianProcesses/GaussianProcessBase.cs
DeepCopy checks whether the parameter count is available before preparing topology. PrepareParameterTopology treats an unavailable destination layout as a no-op. The GaussianProcessBase<T> DeepCopy override is removed, while WithParameters still calls DeepCopy().

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix

Suggested reviewers: franklinic

Merge Risk: 🟡 Moderate · up to 7c1cf

Loading or copying a fitted deep Gaussian process into a differently configured model can leave inconsistent layer state and fail later during training or prediction. Validate fitted layer state before merging.

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Description Check ✅ Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title check ✅ Passed The title accurately summarizes the main changes: persisting DeepGaussianProcess layer state and removing the shallow Gaussian process clone.
Docstring Coverage ✅ Passed Docstring coverage is 85.71% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 3 files.
Linked Issues check ✅ Passed Check skipped because no linked issues were found for this pull request.
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Layers keep their learned state,
Deferred shapes can now await,
Copies cross the waiting gate,
Kuu returns to proper state,
Matrices rest where they relate.

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Actionable comments posted: 1


  • 🪄 Fix CodeRabbit comments on this PR
🤖 Prompt to fix review comments
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
minimal, and validate.

Inline comments:
In `@src/GaussianProcesses/DeepGaussianProcess.cs`:
- Around line 634-639: Update Deserialize’s post-restore flow to validate fitted
layer state before any ComputeKuu calls. In RestoreLayerMatrices, require each
non-null restored list to have exactly _layers.Count entries and restore every
index instead of truncating to the overlap; preserve null lists and all-empty
legacy shells. Add ValidateRestoredLayerState to reject partially initialized or
mixed layers and verify inducing-input, variational-mean, and covariance matrix
dimensions match, throwing InvalidDataException before rebuilding Kuu.

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📒 Files selected for processing (4)
  • src/GaussianProcesses/DeepGaussianProcess.cs
  • src/GaussianProcesses/GaussianProcessBase.cs
  • src/Models/CloneEngine.cs
  • src/Models/ModelBase.cs
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  • src/GaussianProcesses/GaussianProcessBase.cs

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Comment thread src/GaussianProcesses/DeepGaussianProcess.cs Outdated
Comment thread src/GaussianProcesses/DeepGaussianProcess.cs Outdated
Two review findings on the restore path.

1. BLOCKING: validate before rebuilding Kuu.

RestoreLayerMatrices restored only the overlapping prefix
(Math.Min(_layers.Count, restored.Count)), so a checkpoint from a different
architecture left the model holding constructor state in some layers and
checkpoint state in others. Nothing downstream could tell the halves apart:
ComputeKuu reads only InducingInputs and rebuilds happily, then Forward indexes
VariationalMean using the destination layer's dimensions -- so the mixture
surfaced as an index error inside a matrix multiply, or as silently wrong
predictions when the shapes happened to line up. The old doc comment
rationalised this as something "the base class reports on its own terms", which
it does not.

An exact count is now required, and a new ValidateRestoredLayerState runs before
ComputeKuu. Within one fitted layer the inducing-point count m ties the three
matrices together -- InducingInputs [m, inputDim], VariationalMean [m, OutputDim],
VariationalCovCholesky [m, m] -- and they are declared independently, so a
checkpoint can disagree with itself. The validation rejects a half-populated
triple and any of those three shape disagreements, naming the layer and the
actual dimensions.

Unfitted and legacy shells keep loading: a null payload, or one holding only
null and empty matrices, is the absence of state rather than a disagreement
about shape, and is left alone.

2. CodeQL, missed opportunity to use Where.

The Kuu rebuild loop filtered inside its body. The condition is now part of the
sequence.

Build: src/AiDotNet.csproj -f net10.0, 0 errors.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

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