# Documentation

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# icdf

Class: prob.TruncatableDistribution
Package: prob

Inverse cumulative distribution function of probability distribution object

## Syntax

`y = icdf(pd,prob)`

## Description

`y = icdf(pd,prob)` returns the inverse cumulative distribution function (icdf) values of the probability distribution `pd` at the probabilities in `prob`.

## Input Arguments

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Probability distribution, specified as a probability distribution object. Create a probability distribution object with specified parameter values using `makedist`. Alternatively, for fittable distributions, create a probability distribution object by fitting it to data using `fitdist` or the Distribution Fitting app.

Probabilities at which to compute the icdf, specified as an array of scalar values in the range [0,1]. For example, specifying ```[.25 .5 .75]``` returns a vector containing three icdf values corresponding to these probabilities.

Data Types: `single` | `double`

## Output Arguments

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Inverse cumulative distribution function (icdf) values of the specified probability distribution, evaluated at the probabilities in `prob`, returned as an array. `y` has the same dimensions as `x`.

## Examples

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Create a standard normal distribution object.

`pd = makedist('Normal')`
```pd = NormalDistribution Normal distribution mu = 0 sigma = 1```

Determine the critical values at the 5% significance level for a test statistic with a standard normal distribution, by computing the upper and lower 2.5% values.

`y = icdf(pd,[.025,.975])`
```y = -1.9600 1.9600```

Plot the cdf and shade the critical regions.

`p = normspec(y,0,1,'outside')`