@stdlib/stats/base/dists/t/ctor/README.md

Standard library statistical functions.

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# Student's T

> Student's t distribution constructor.

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## Usage

```javascript
var T = require( '@stdlib/stats/base/dists/t/ctor' );
```

#### T( \[v] )

Returns a [Student's t][t-distribution] distribution object.

```javascript
var t = new T();

var mu = t.mean;
// returns NaN
```

By default, `v = 1.0`. To create a distribution having a different degrees of freedom `v`, provide a parameter value.

```javascript
var t = new T( 4.0 );

var mu = t.mean;
// returns 0.0
```

* * *

## t

A [Student's t][t-distribution] distribution object has the following properties and methods...

### Writable Properties

#### t.v

Degrees of freedom of the distribution. `v` **must** be a positive number.

```javascript
var t = new T( 2.0 );

var v = t.v;
// returns 2.0

t.v = 3.0;

v = t.v;
// returns 3.0
```

* * *

### Computed Properties

#### T.prototype.entropy

Returns the [differential entropy][entropy].

```javascript
var t = new T( 4.0 );

var entropy = t.entropy;
// returns ~1.682
```

#### T.prototype.kurtosis

Returns the [excess kurtosis][kurtosis].

```javascript
var t = new T( 4.0 );

var kurtosis = t.kurtosis;
// returns Infinity
```

#### T.prototype.mean

Returns the [expected value][expected-value].

```javascript
var t = new T( 4.0 );

var mu = t.mean;
// returns 0.0
```

#### T.prototype.median

Returns the [median][median].

```javascript
var t = new T( 4.0 );

var median = t.median;
// returns 0.0
```

#### T.prototype.mode

Returns the [mode][mode].

```javascript
var t = new T( 4.0 );

var mode = t.mode;
// returns 0.0
```

#### T.prototype.skewness

Returns the [skewness][skewness].

```javascript
var t = new T( 4.0 );

var skewness = t.skewness;
// returns 0.0
```

#### T.prototype.stdev

Returns the [standard deviation][standard-deviation].

```javascript
var t = new T( 4.0 );

var s = t.stdev;
// returns ~1.414
```

#### T.prototype.variance

Returns the [variance][variance].

```javascript
var t = new T( 4.0 );

var s2 = t.variance;
// returns 2.0
```

* * *

### Methods

#### T.prototype.cdf( x )

Evaluates the [cumulative distribution function][cdf] (CDF).

```javascript
var t = new T( 2.0 );

var y = t.cdf( 0.5 );
// returns ~0.667
```

#### T.prototype.logcdf( x )

Evaluates the natural logarithm of the [cumulative distribution function][cdf] (CDF).

```javascript
var t = new T( 2.0 );

var y = t.logcdf( 0.5 );
// returns ~-0.405
```

#### T.prototype.logpdf( x )

Evaluates the natural logarithm of the [probability density function][pdf] (PDF).

```javascript
var t = new T( 2.0 );

var y = t.logpdf( 0.8 );
// returns ~-1.456
```

#### T.prototype.pdf( x )

Evaluates the [probability density function][pdf] (PDF).

```javascript
var t = new T( 2.0 );

var y = t.pdf( 0.8 );
// returns ~0.233
```

#### T.prototype.quantile( p )

Evaluates the [quantile function][quantile-function] at probability `p`.

```javascript
var t = new T( 2.0 );

var y = t.quantile( 0.5 );
// returns 0.0

y = t.quantile( 1.9 );
// returns NaN
```

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* * *

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## Examples

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```javascript
var T = require( '@stdlib/stats/base/dists/t/ctor' );

var t = new T( 2.0 );

var mu = t.mean;
// returns 0.0

var mode = t.mode;
// returns 0.0

var s2 = t.variance;
// returns Infinity

var y = t.cdf( 0.8 );
// returns ~0.746
```

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[t-distribution]: https://en.wikipedia.org/wiki/Student%27s_t-distribution

[cdf]: https://en.wikipedia.org/wiki/Cumulative_distribution_function

[pdf]: https://en.wikipedia.org/wiki/Probability_density_function

[quantile-function]: https://en.wikipedia.org/wiki/Quantile_function

[entropy]: https://en.wikipedia.org/wiki/Entropy_%28information_theory%29

[expected-value]: https://en.wikipedia.org/wiki/Expected_value

[kurtosis]: https://en.wikipedia.org/wiki/Kurtosis

[median]: https://en.wikipedia.org/wiki/Median

[mode]: https://en.wikipedia.org/wiki/Mode_%28statistics%29

[skewness]: https://en.wikipedia.org/wiki/Skewness

[standard-deviation]: https://en.wikipedia.org/wiki/Standard_deviation

[variance]: https://en.wikipedia.org/wiki/Variance

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