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Latent semantic analysis

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Latent Semantic Analysis (LSA)
– LSA is a technique in natural language processing that analyzes relationships between documents and the terms they contain.
– LSA uses a matrix of word counts per document and singular value decomposition (SVD).
– Documents are compared using cosine similarity.
– LSA can be used for topic detection and latent component identification.
– LSA can use a document-term matrix to describe term occurrences in documents.
– The matrix is typically weighted using tf-idf.
– LSA groups documents and words with similar occurrences.
– LSA finds a low-rank approximation to the term-document matrix.
– Approximations are used to handle large matrices or noisy data.
– Rank lowering combines dimensions and reduces noise.
– Rank lowering helps identify synonymy and mitigate polysemy.
– Rank lowering merges dimensions with similar meanings.
– LSA uses a matrix to describe term occurrences in documents.
– Singular value decomposition (SVD) is applied to the matrix.
– The k largest singular values and their corresponding vectors are selected.
– The approximation of the matrix in a lower-dimensional space is obtained.
– Documents and terms can be compared and clustered using the low-dimensional space.
– LSA can be used for data clustering and document classification.
– LSA enables cross-language information retrieval by analyzing translated documents.
– LSA helps find relations between documents and terms.
– LSA can be used for query-based document retrieval.
– LSA provides a low-dimensional space for analyzing document similarities.

Synonymy and Polysemy in Natural Language Processing
– Synonymy is the phenomenon where different words describe the same idea.
– Polysemy is the phenomenon where the same word has multiple meanings.
– Synonymy and polysemy pose challenges in search engines and information retrieval.
– A search engine may fail to retrieve relevant documents due to synonymy.
– A search may retrieve irrelevant documents due to polysemy.

Commercial Applications
– LSA has been used to assist in performing prior art searches for patents.
– LSA can help in analyzing and retrieving relevant information for commercial purposes.
– LSA can be applied in various industries, such as finance, marketing, and healthcare.
– LSA can improve search engine algorithms for better user experience.
– LSA can enhance recommendation systems for personalized product suggestions.

Applications in Human Memory
– LSA has been prevalent in the study of human memory, particularly in areas of free recall and memory search.
– There is a positive correlation between the semantic similarity of words (measured by LSA) and the probability of recall in free recall tasks.
– Mistakes in recalling studied items tend to be semantically related to the desired item.
– LSA can be used to study word associations and relatedness in memory experiments.
– Word Association Spaces (WAS) is another model used in memory studies.

Implementation, Limitations, and Alternative Methods
– Singular Value Decomposition (SVD) is typically used to compute LSA.
– Large matrix methods, such as Lanczos methods, are used for SVD computation.
– Incremental and low-memory approaches, like neural network-like methods, can also compute SVD.
– Fast algorithms for LSA implementation are available in MATLAB and Python.
– Parallel ARPACK algorithm can speed up SVD computation while maintaining prediction quality.
– LSA dimensions can be difficult to interpret and lack immediate meaning in natural language.
– LSA partially captures polysemy and struggles with multiple meanings of a word.
– Bag of Words (BOW) model has limitations that can be addressed using multi-gram dictionaries.
– Probabilistic Latent Semantic Analysis (PLSA) is an alternative to LSA, based on a multinomial model.
– Semantic Hashing is another method that uses neural networks for efficient document retrieval.

Latent semantic analysis (LSA) is a technique in natural language processing, in particular distributional semantics, of analyzing relationships between a set of documents and the terms they contain by producing a set of concepts related to the documents and terms. LSA assumes that words that are close in meaning will occur in similar pieces of text (the distributional hypothesis). A matrix containing word counts per document (rows represent unique words and columns represent each document) is constructed from a large piece of text and a mathematical technique called singular value decomposition (SVD) is used to reduce the number of rows while preserving the similarity structure among columns. Documents are then compared by cosine similarity between any two columns. Values close to 1 represent very similar documents while values close to 0 represent very dissimilar documents.

An information retrieval technique using latent semantic structure was patented in 1988 (US Patent 4,839,853, now expired) by Scott Deerwester, Susan Dumais, George Furnas, Richard Harshman, Thomas Landauer, Karen Lochbaum and Lynn Streeter. In the context of its application to information retrieval, it is sometimes called latent semantic indexing (LSI).

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