e7f9710499
* Fix typo in a variable name in example code. * Rename df2dx2 to d2fdx2 - the appropriate naming for the second derivative * Update CONTRIBUTING.md - add needed python packages, and a virtual-env hint * Revert "Fix typo in a variable name in example code." This reverts commit bc10a175345c3e20eab689c47f7d866073a3c233. * Rename df2dx2 to d2fdx2