AIMech AI

Probabilistic latent semantic analysis

Model Families AIMech:ProbabilisticLatentSemanticAnalysis DRAFT
Aliases: PLSA, Probabilistic latent semantic indexing, PLSI
A latent-class model of document–word or other dyadic co-occurrences that represents their joint probability as a mixture of conditionally independent distributions over the two observed entities.
Identity Notes & Concept Scope PLSA denotes the aspect-model probability construction, also called the probabilistic latent semantic indexing model in the LDA comparison. A document can mix several aspects because each co-occurrence has its own latent class. It differs from an SVD reconstruction, a single class for a whole document, and LDA’s prior over document-specific topic weights. The alias PLSI identifies this underlying model, not every cosine, interpolation or model-averaging choice in a retrieval pipeline. Tempered EM is one fitting procedure rather than part of the model’s defining probability law. Compared all 442 pinned AIO labels and scoped synonyms and 418 preceding native IDs, names and aliases. The initial normalized LDA hit denotes LinearDiscriminantAnalysis, whose full Gaussian-classifier record was read; the bare LDA alias is omitted from the new topic-model record. No normalized identity match remains for the final candidate names/aliases. Final full-checkout fixed-string searches, including ignored and hidden files in both worktree and main, return two lines each; both unique contents are existing frontier references. An additional broad LDA search returned 289 worktree and 237 main lines before the preceding batch merged; all 84 distinct contents were read, covering the existing classifier, topic-context references, unrelated programming mnemonics and namespace abbreviations. All 188 semantic label/synonym hits were read. Nineteen exact annotated AIO CLASS nodes and outgoing edges were inspected (18 verified unchanged from prior reading, Biclustering read here), along with their generated records and 16 native neighbors. The 35 contextual YAMLs were read or byte-verified after documented full reading. Absence is bounded to this snapshot, maintained corpus and inspected semantic neighborhood.

Claims & Grounded Evidence

1 Claim
Mechanism #method
For finite document indices d, vocabulary items w and K latent classes z, choose normalized nonnegative distributions pi_z, a_z(d) and b_z(w), and define p(d,w)=sum_z pi_z*a_z(d)*b_z(w). Given z, d and w are independent. Equivalently, for p(d)>0, p(w|d)=sum_z theta_dz*b_z(w), where theta_dz=pi_z*a_z(d)/p(d). Fit observed counts n(d,w) with sum_dw n(d,w)*log p(d,w). An exact EM E-step computes r_dwz=pi_z*a_z(d)*b_z(w)/p(d,w); M-steps normalize the corresponding count-weighted responsibilities over words, documents and classes. Each conditional document word distribution is an arithmetic convex combination of topic probabilities. In the original fold-in procedure, keep b_z(w) fixed and fit a new query or document’s mixture weights. This introduces new fitted weights rather than integrating over a population prior as in LDA.

⚠️ Curated Limitations & Negative Results

Artificial Intelligence Ontology (AIO) Grounding

Mapped AIO Classes
AIO Target Class Mapping Relation Mapping Rationale
AIO:Model
Model
broad_match The local concept specifies a mathematical probability model and is narrower than the pinned generic Model class. This is a local scope assessment, not an upstream assertion.
AIO:ProbabilisticTopicModel
Probabilistic Topic Model
related_match The local model describes latent topic distributions. The inspected AIO target lies in MachineLearningTask and is phrased as analyzing word themes; related match preserves the model-to-task distinction without asserting an is-a relation or temporal dynamics.

Evidence Sources & Primary Literature

2 Sources
Source ID Publication / Document Type / Access Reference & Checksum
method-source
Thomas Hofmann
primary paper
full_text
ID: arXiv:1301.6705v1
sha256:798ce8b95d01…
model-comparison
David M. Blei, Andrew Y. Ng, Michael I. Jordan
primary paper
full_text
ID: https://www.jmlr.org/papers/v3/blei03a.html
sha256:4667de63545b…

Curation Provenance

Curator: Codex
Method: ai_assisted
Model: GPT-6
Created: 2026-10-11T23:19:29Z
Updated: 2026-10-11T23:20:15Z
Source File: data/curated/ProbabilisticLatentSemanticAnalysis.yaml