DTLZ7

[dongzhiming]

Hi, DTLZ7 does not implement the '_calc_pareto_front' method.

[blankjul]

yes so far I added only for the problems with a linear or spherical pareto front.
I will have a look if I do have the mathematical expression for the front somewhere...
If you are planning to implement it by yourself, feel free to send it to me via email or directly create a pull request.

Julian