MIT License

Copyright (c) 2015 Samsy - https://codepen.io/Samsy/pen/GpXXEj
Copyright (C) 2011 Ashima Arts (Simplex noise)
Copyright (C) 2011-2016 Stefan Gustavson (Classic noise and others)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

Source: Samsy's public CodePen, #Codevember Day 6 Derivate Curl Noise,
https://codepen.io/Samsy/pen/GpXXEj
Public Pen licensing: https://blog.codepen.io/documentation/licensing/
Corresponding author gist: https://gist.github.com/Samsy/ce0802c2dbded8511fda

Only the reusable simplexNoiseDerivatives function is included in this
vendor unit. The corresponding gist alone has no explicit license file;
reuse relies on the identical function published in the public MIT Pen.
The attribution above records the Pen author and 2015 publication evidence
from the matching author gist, not an assertion that a per-Pen notice was
visible in the retrieved preview HTML.