feat: add wald distribution namespace

lib/node_modules/@stdlib/stats/base/dists/wald/README.md

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+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2026 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.
+You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+-->
+
+# Wald
+
+> Wald distribution.
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var wald = require( '@stdlib/stats/base/dists/wald' );
+```
+
+#### wald
+
+[Wald][wald-distribution] (inverse Gaussian) distribution.
+
+```javascript
+var dist = wald;
+// returns {...}
+```
+
+The namespace contains the following distribution functions:
+
+<!-- <toc pattern="*+(cdf|pdf|mgf|quantile)*"> -->
+
+<div class="namespace-toc">
+
+-   <span class="signature">[`cdf( x, mu, lambda )`][@stdlib/stats/base/dists/wald/cdf]</span><span class="delimiter">: </span><span class="description">Wald distribution cumulative distribution function.</span>
+-   <span class="signature">[`logcdf( x, mu, lambda )`][@stdlib/stats/base/dists/wald/logcdf]</span><span class="delimiter">: </span><span class="description">Wald distribution natural logarithm of cumulative distribution function.</span>
+-   <span class="signature">[`logpdf( x, mu, lambda )`][@stdlib/stats/base/dists/wald/logpdf]</span><span class="delimiter">: </span><span class="description">Wald distribution natural logarithm of probability density function (PDF).</span>
+-   <span class="signature">[`mgf( t, mu, lambda )`][@stdlib/stats/base/dists/wald/mgf]</span><span class="delimiter">: </span><span class="description">Wald distribution moment-generating function (MGF).</span>
+-   <span class="signature">[`pdf( x, mu, lambda )`][@stdlib/stats/base/dists/wald/pdf]</span><span class="delimiter">: </span><span class="description">Wald distribution probability density function (PDF).</span>
+-   <span class="signature">[`quantile( p, mu, lambda )`][@stdlib/stats/base/dists/wald/quantile]</span><span class="delimiter">: </span><span class="description">Wald distribution quantile function.</span>
+
+</div>
+
+<!-- </toc> -->
+
+The namespace contains the following functions for calculating distribution properties:
+
+<!-- <toc pattern="*+(kurtosis|mean|mode|skewness|stdev|variance)*"> -->
+
+<div class="namespace-toc">
+
+-   <span class="signature">[`kurtosis( mu, lambda )`][@stdlib/stats/base/dists/wald/kurtosis]</span><span class="delimiter">: </span><span class="description">Wald distribution excess kurtosis.</span>
+-   <span class="signature">[`mean( mu, lambda )`][@stdlib/stats/base/dists/wald/mean]</span><span class="delimiter">: </span><span class="description">Wald distribution expected value.</span>
+-   <span class="signature">[`mode( mu, lambda )`][@stdlib/stats/base/dists/wald/mode]</span><span class="delimiter">: </span><span class="description">Wald distribution mode.</span>
+-   <span class="signature">[`skewness( mu, lambda )`][@stdlib/stats/base/dists/wald/skewness]</span><span class="delimiter">: </span><span class="description">Wald distribution skewness.</span>
+-   <span class="signature">[`stdev( mu, lambda )`][@stdlib/stats/base/dists/wald/stdev]</span><span class="delimiter">: </span><span class="description">Wald distribution standard deviation.</span>
+-   <span class="signature">[`variance( mu, lambda )`][@stdlib/stats/base/dists/wald/variance]</span><span class="delimiter">: </span><span class="description">Wald distribution variance.</span>
+
+</div>
+
+<!-- </toc> -->
+
+</section>
+
+<!-- /.usage -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var wald = require( '@stdlib/stats/base/dists/wald' );
+
+/*
+* The Wald (inverse Gaussian) distribution is parameterized by mean `mu` and shape parameter `lambda`.
+*/
+
+var mu = 20.0;
+var lambda = 60.0;
+
+// Compute the mean:
+var m = wald.mean( mu, lambda );
+// returns 20.0
+
+// Compute the mode:
+var md = wald.mode( mu, lambda );
+// returns ~12.361
+
+// Compute the variance:
+var s2 = wald.variance( mu, lambda );
+// returns ~133.333
+
+// Compute the standard deviation:
+var sigma = wald.stdev( mu, lambda );
+// returns ~11.547
+
+// Compute the skewness:
+var skew = wald.skewness( mu, lambda );
+// returns ~1.732
+
+// Compute the excess kurtosis:
+var kappa = wald.kurtosis( mu, lambda );
+// returns 5.0
+
+// Evaluate the PDF at x = 20.0:
+var y = wald.pdf( 20.0, mu, lambda );
+// returns ~0.0345
+
+// Evaluate the CDF at x = 20.0:
+var p = wald.cdf( 20.0, mu, lambda );
+// returns ~0.607
+
+// Evaluate the logPDF at x = 20.0:
+var ly = wald.logpdf( 20.0, mu, lambda );
+// returns ~-3.365
+
+// Evaluate the logCDF at x = 20.0:
+var lp = wald.logcdf( 20.0, mu, lambda );
+// returns ~-0.499
+
+// Compute the 50th percentile:
+var q = wald.quantile( 0.5, mu, lambda );
+// returns ~17.193
+
+// Evaluate the MGF at t = 0.01:
+var m0 = wald.mgf( 0.01, mu, lambda );
+// returns ~1.23
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+</section>
+
+<!-- /.related -->
+
+<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="links">
+
+[wald-distribution]: https://en.wikipedia.org/wiki/Inverse_Gaussian_distribution
+
+<!-- <toc-links> -->
+
+[@stdlib/stats/base/dists/wald/kurtosis]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/kurtosis
+
+[@stdlib/stats/base/dists/wald/mean]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/mean
+
+[@stdlib/stats/base/dists/wald/mode]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/mode
+
+[@stdlib/stats/base/dists/wald/skewness]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/skewness
+
+[@stdlib/stats/base/dists/wald/stdev]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/stdev
+
+[@stdlib/stats/base/dists/wald/variance]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/variance
+
+[@stdlib/stats/base/dists/wald/cdf]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/cdf
+
+[@stdlib/stats/base/dists/wald/logcdf]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/logcdf
+
+[@stdlib/stats/base/dists/wald/logpdf]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/logpdf
+
+[@stdlib/stats/base/dists/wald/mgf]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/mgf
+
+[@stdlib/stats/base/dists/wald/pdf]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/pdf
+
+[@stdlib/stats/base/dists/wald/quantile]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists/wald/quantile
+
+<!-- </toc-links> -->
+
+</section>
+
+<!-- /.links -->