# Documentation

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# plotDiagnostics

Class: GeneralizedLinearModel

Plot diagnostics of generalized linear regression model

## Syntax

`plotDiagnostics(mdl)plotDiagnostics(mdl,plottype)h = plotDiagnostics(...)h = plotDiagnostics(mdl,plottype,Name,Value)`

## Description

`plotDiagnostics(mdl)` plots diagnostics from the `mdl` linear model using leverage as the plot type.

`plotDiagnostics(mdl,plottype)` plots diagnostics from the `mdl` generalized linear model in a plot of type `plottype`.

`h = plotDiagnostics(...)` returns handles to the lines in the plot.

`h = plotDiagnostics(mdl,plottype,Name,Value)` plots with additional options specified by one or more `Name,Value` pair arguments.

## Input Arguments

`mdl`

Generalized linear model, as constructed by `fitglm` or `stepwiseglm`.

`plottype`

Character vector specifying the type of plot:

 `'contour'` Residual vs. leverage with overlayed Cook's contours `'cookd'` Cook's distance `'leverage'` Leverage (diagonal of Hat matrix)

Default: `'leverage'`

### Name-Value Pair Arguments

Specify optional comma-separated pairs of `Name,Value` arguments. `Name` is the argument name and `Value` is the corresponding value. `Name` must appear inside single quotes (`' '`). You can specify several name and value pair arguments in any order as `Name1,Value1,...,NameN,ValueN`.

 Note:   The plot property name-value pairs apply to the first returned handle `h(1)`.
 `'Color'` Color of the line or marker, a `ColorSpec` specification. For details, see `linespec`. `'LineStyle'` Type of line, a Chart Line Properties specification. For details, see `linespec`. `'LineWidth'` Width of the line or edges of filled area, in points, a positive scalar. One point is 1/72 inch. Default: `0.5` `'MarkerEdgeColor'` Color of the marker or edge color for filled markers, a `ColorSpec` specification. For details, see `linespec`. `'MarkerFaceColor'` Color of the marker face for filled markers, a `ColorSpec` specification. For details, see `linespec`. `'MarkerSize'` Size of the marker in points, a strictly positive scalar. One point is 1/72 inch.

## Output Arguments

 `h` Vector of handles to lines or patches in the plot.

## Examples

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Create leverage and Cook's distance plots of a fitted generalized linear model.

Generate artificial data for the model, Poisson random numbers with two underlying predictors `X(1)` and `X(2)`.

```rng default % for reproducibility rndvars = randn(100,2); X = [2+rndvars(:,1),rndvars(:,2)]; mu = exp(1 + X*[1;2]); y = poissrnd(mu); ```

Create a generalized linear regression model of Poisson data.

```mdl = fitglm(X,y,'y ~ x1 + x2','distr','poisson'); ```

Create a leverage plot.

```plotDiagnostics(mdl) ```

Create a contour plot with Cook's distance.

```plotDiagnostics(mdl,'contour') ```

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## Tips

• For many plots, the Data Cursor tool in the figure window displays the x and y values for any data point, along with the observation name or number.

## References

[1] Neter, J., M. H. Kutner, C. J. Nachtsheim, and W. Wasserman. Applied Linear Statistical Models, Fourth Edition. Irwin, Chicago, 1996.