# resubMargin

Resubstitution classification margin

## Description

returns the resubstitution Classification Margin (`m`

= resubMargin(`Mdl`

)`m`

) for
the trained classification model `Mdl`

using the predictor data stored in
`Mdl.X`

and the corresponding true class labels stored in
`Mdl.Y`

.

`m`

is returned as an *n*-by-1 numeric column
vector, where *n* is the number of observations in the predictor
data.

specifies whether to include interaction terms in computations. This syntax applies only to
generalized additive models.`m`

= resubMargin(`Mdl`

,'IncludeInteractions',`includeInteractions`

)

## Examples

### Estimate Resubstitution Classification Margins of Naive Bayes Classifier

Estimate the resubstitution (in-sample) classification margins of a naive Bayes classifier. An observation margin is the observed true class score minus the maximum false class score among all scores in the respective class.

Load the `fisheriris`

data set. Create `X`

as a numeric matrix that contains four measurements for 150 irises. Create `Y`

as a cell array of character vectors that contains the corresponding iris species.

```
load fisheriris
X = meas;
Y = species;
```

Train a naive Bayes classifier using the predictors `X`

and class labels `Y`

. A recommended practice is to specify the class names. `fitcnb`

assumes that each predictor is conditionally and normally distributed.

Mdl = fitcnb(X,Y,'ClassNames',{'setosa','versicolor','virginica'})

Mdl = ClassificationNaiveBayes ResponseName: 'Y' CategoricalPredictors: [] ClassNames: {'setosa' 'versicolor' 'virginica'} ScoreTransform: 'none' NumObservations: 150 DistributionNames: {'normal' 'normal' 'normal' 'normal'} DistributionParameters: {3x4 cell} Properties, Methods

`Mdl`

is a trained `ClassificationNaiveBayes`

classifier.

Estimate the resubstitution classification margins.

m = resubMargin(Mdl); median(m)

ans = 1.0000

Display the histogram of the in-sample classification margins.

histogram(m,30,'Normalization','probability') xlabel('In-Sample Margins') ylabel('Probability') title('Probability Distribution of the In-Sample Margins')

Classifiers that yield relatively large margins are preferred.

### Select SVM Classifier Features by Examining In-Sample Margins

Perform feature selection by comparing in-sample margins from multiple models. Based solely on this comparison, the model with the highest margins is the best model.

Load the `ionosphere`

data set. Define two data sets:

`fullX`

contains all predictors (except the removed column of 0s).`partX`

contains the last 20 predictors.

```
load ionosphere
fullX = X;
partX = X(:,end-20:end);
```

Train a support vector machine (SVM) classifier for each predictor set.

FullSVMModel = fitcsvm(fullX,Y); PartSVMModel = fitcsvm(partX,Y);

Estimate the in-sample margins for each classifier.

fullMargins = resubMargin(FullSVMModel); partMargins = resubMargin(PartSVMModel); n = size(X,1); p = sum(fullMargins < partMargins)/n

p = 0.2251

Approximately 22% of the margins from the full model are less than those from the model with fewer predictors. This result suggests that the model trained with all the predictors is better.

### Compare GAMs by Examining Training Sample Margins and Edge

Compare a generalized additive model (GAM) with linear terms to a GAM with both linear and interaction terms by examining the training sample margins and edge. Based solely on this comparison, the classifier with the highest margins and edge is the best model.

Load the 1994 census data stored in `census1994.mat`

. The data set consists of demographic data from the US Census Bureau to predict whether an individual makes over $50,000 per year. The classification task is to fit a model that predicts the salary category of people given their age, working class, education level, marital status, race, and so on.

`load census1994`

`census1994`

contains the training data set `adultdata`

and the test data set `adulttest`

. To reduce the running time for this example, subsample 500 training observations from `adultdata`

by using the `datasample`

function.

rng('default') % For reproducibility NumSamples = 5e2; adultdata = datasample(adultdata,NumSamples,'Replace',false);

Train a GAM that contains both linear and interaction terms for predictors. Specify to include all available interaction terms whose *p*-values are not greater than 0.05.

Mdl = fitcgam(adultdata,'salary','Interactions','all','MaxPValue',0.05)

Mdl = ClassificationGAM PredictorNames: {1x14 cell} ResponseName: 'salary' CategoricalPredictors: [2 4 6 7 8 9 10 14] ClassNames: [<=50K >50K] ScoreTransform: 'logit' Intercept: -32.0842 Interactions: [82x2 double] NumObservations: 500 Properties, Methods

`Mdl`

is a `ClassificationGAM`

model object. `Mdl`

includes 82 interaction terms.

Estimate the training sample margins and edge for `Mdl`

.

M = resubMargin(Mdl); E = resubEdge(Mdl)

E = 1.0000

Estimate the training sample margins and edge for `Mdl`

without including interaction terms.

M_nointeractions = resubMargin(Mdl,'IncludeInteractions',false); E_nointeractions = resubEdge(Mdl,'IncludeInteractions',false)

E_nointeractions = 0.9516

Display the distributions of the margins using box plots.

boxplot([M M_nointeractions],'Labels',{'Linear and Interaction Terms','Linear Terms Only'}) title('Box Plots of Training Sample Margins')

When you include the interaction terms in the computation, all the resubstitution margin values for `Mdl`

are 1, and the resubstitution edge value (average of the margins) is 1. The margins and edge decrease when you do not include the interaction terms in `Mdl`

.

## Input Arguments

`Mdl`

— Classification machine learning model

full classification model object

Classification machine learning model, specified as a full classification model object, as given in the following table of supported models.

Model | Classification Model Object |
---|---|

Generalized additive model | `ClassificationGAM` |

k-nearest neighbor model | `ClassificationKNN` |

Naive Bayes model | `ClassificationNaiveBayes` |

Neural network model | `ClassificationNeuralNetwork` |

Support vector machine for one-class and binary classification | `ClassificationSVM` |

`includeInteractions`

— Flag to include interaction terms

`true`

| `false`

Flag to include interaction terms of the model, specified as `true`

or
`false`

. This argument is valid only for a generalized
additive model (GAM). That is, you can specify this argument only when
`Mdl`

is `ClassificationGAM`

.

The default value is `true`

if `Mdl`

contains interaction
terms. The value must be `false`

if the model does not contain interaction
terms.

**Data Types: **`logical`

## More About

### Classification Margin

The *classification margin* for binary classification
is, for each observation, the difference between the classification score for the
true class and the classification score for the false class. The
*classification margin* for multiclass classification
is the difference between the classification score for the true class and the
maximal classification score for the false classes.

If the margins are on the same scale (that is, the score values are based on the same score transformation), then they serve as a classification confidence measure. Among multiple classifiers, those that yield greater margins are better.

## Algorithms

`resubMargin`

computes the classification margin according to the
corresponding `margin`

function of the object (`Mdl`

).
For a model-specific description, see the `margin`

function reference pages
in the following table.

Model | Classification Model Object (`Mdl` ) | `margin` Object Function |
---|---|---|

Generalized additive model | `ClassificationGAM` | `margin` |

k-nearest neighbor model | `ClassificationKNN` | `margin` |

Naive Bayes model | `ClassificationNaiveBayes` | `margin` |

Neural network model | `ClassificationNeuralNetwork` | `margin` |

Support vector machine for one-class and binary classification | `ClassificationSVM` | `margin` |

## Extended Capabilities

### GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

Usage notes and limitations:

This function fully supports GPU arrays for a trained classification model specified as a

`ClassificationKNN`

or`ClassificationSVM`

object.

For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

## See Also

**Introduced in R2012a**

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