time-to-botec/js/node_modules/@stdlib/math/base/special/digamma/README.md

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@license Apache-2.0
Copyright (c) 2018 The Stdlib Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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# digamma
> [Digamma][digamma-function] function.
<section class="intro">
The [digamma function][digamma-function] `ψ` is the logarithmic derivative of the [gamma function][gamma-function], i.e.
<!-- <equation class="equation" label="eq:digamma_function" align="center" raw="\psi(x) =\frac{d}{dx} \ln{\Gamma(x)}= \frac{\Gamma\,'(x)}{\Gamma(x)}" alt="Digamma function"> -->
<div class="equation" align="center" data-raw-text="\psi(x) =\frac{d}{dx} \ln{\Gamma(x)}= \frac{\Gamma\,&#39;(x)}{\Gamma(x)}" data-equation="eq:digamma_function">
<img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@bb29798906e119fcb2af99e94b60407a270c9b32/lib/node_modules/@stdlib/math/base/special/digamma/docs/img/equation_digamma_function.svg" alt="Digamma function">
<br>
</div>
<!-- </equation> -->
</section>
<!-- /.intro -->
<section class="usage">
## Usage
```javascript
var digamma = require( '@stdlib/math/base/special/digamma' );
```
#### digamma( x )
Evaluates the [digamma function][digamma-function].
```javascript
var v = digamma( -2.5 );
// returns ~1.103
v = digamma( 1.0 );
// returns ~-0.577
v = digamma( 10.0 );
// returns ~2.252
```
If `x` is `0` or a negative `integer`, the function returns `NaN`.
```javascript
var v = digamma( 0.0 );
// returns NaN
v = digamma( -1.0 );
// returns NaN
v = digamma( -2.0 );
// returns NaN
```
If provided `NaN`, the function returns `NaN`.
```javascript
var v = digamma( NaN );
// returns NaN
```
</section>
<!-- /.usage -->
<section class="examples">
## Examples
<!-- eslint no-undef: "error" -->
```javascript
var randu = require( '@stdlib/random/base/randu' );
var digamma = require( '@stdlib/math/base/special/digamma' );
var x;
var v;
var i;
for ( i = 0; i < 10; i++ ) {
x = (randu()*10.0) - 5.0;
v = digamma( x );
console.log( 'x: %d, f(x): %d', x, v );
}
```
</section>
<!-- /.examples -->
<section class="links">
[digamma-function]: https://en.wikipedia.org/wiki/Digamma_function
[gamma-function]: https://en.wikipedia.org/wiki/Gamma_function
</section>
<!-- /.links -->