XSqrA_M (Terrier Information Retrieval Platform 5.5 API)

java.lang.Object
- org.terrier.matching.models.WeightingModel
- - org.terrier.matching.models.XSqrA_M

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, Model
```
public class XSqrA_M
extends WeightingModel
```
This class implements the XSqrA_M weighting model, which computed the inner product of Pearson's X^2 with the information growth computed with the multinomial M. It is an unsupervised DFR model of IR (free from parameters), which can be used on short or medium verbose queries.
XSqrA_M has a high performance, and in particular has statistically significant better MAP performance than all other supervised models on the GOV2 collection. MAP for short (title only) and medium (title+description) topics, and comparative p values (two-tailed paired t-test) compared to supervised models (with optimal MAP parameter values) are as follows:

Queries MAP of XSqrA_M LGD Dirichlet_LM PL2 BM25 In_expB2

short 0.3156 p=0.3277 p=0.0075 p=0.0055 p=0.0064 p=0.0002

medium 0.3311 p=2.3E-07 p=0.0002 p=0.0395 p=0.0025 p=2.4E-10

References Frequentist and Bayesian approach to Information Retrieval. G. Amati. In Proceedings of the 28th European Conference on IR Research (ECIR 2006). LNCS vol 3936, pages 13--24.

Since:

3.5

Author:

Gianni Amati

See Also:

Serialized Form

Field Summary
- Fields inherited from class org.terrier.matching.models.WeightingModel
  averageDocumentLength, c, cs, documentFrequency, es, i, keyFrequency, numberOfDocuments, numberOfPointers, numberOfPostings, numberOfTokens, numberOfUniqueTerms, rq, termFrequency

Constructor Summary

Constructors
Constructor Description

XSqrA_M()
A default constructor to make this model.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`java.lang.String`	`getInfo()`	Returns the name of the model, in this case "XSqrA_M"
`double`	`score(double tf, double docLength)`	Uses XSqrA_M to compute a weight for a term in a document.

Methods inherited from class org.terrier.matching.models.WeightingModel
clone, getOverflowed, getParameter, prepare, score, setCollectionStatistics, setEntryStatistics, setKeyFrequency, setParameter, setRequest

Methods inherited from class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - XSqrA_M
```
public XSqrA_M()
```
    A default constructor to make this model.
- Method Detail
  - getInfo
```
public final java.lang.String getInfo()
```
    Returns the name of the model, in this case "XSqrA_M"
    
    Specified by:
    
    getInfo in interface Model
    
    Specified by:
    
    getInfo in class WeightingModel
    
    Returns:
    
    the name of the model
  - score
```
public final double score(double tf,
                          double docLength)
```
    Uses XSqrA_M to compute a weight for a term in a document.
    
    Specified by:
    
    score in class WeightingModel
    
    Parameters:
    
    tf - The term frequency of the term in the document
    
    docLength - the document's length
    
    Returns:
    
    the score assigned to a document with the given tf and docLength, and other preset parameters