[Describe your changes and what you've already done to test it.]

#### Check all that apply (change to `[x]`)
- [ ] All changes meet [libigl style-guidelines](https://libigl.github.io/style-guidelines/).
- [ ] Adds new .cpp file.
- [ ] Adds corresponding unit test.
- [ ] Adds corresponding python binding.
- [ ] This is a minor change.
