travel_time with order==2 has failed

[espdev]

Currently, order == 2 for computing travel time in scikit-fmm (v 2019.1.30) has a numerical issue and does not work properly: scikit-fmm/scikit-fmm#28

The following code should be removed after fixing the issue in scikit-fmm:

scikit-mpe/skmpe/_parameters.py

Lines 40 to 47 in 59551ba

	@validator('travel_time_order')
	def _check_travel_time_order(cls, v):
	if v == TravelTimeOrder.second:
	raise ValueError(
	'Currently the second order for computing travel time does not work properly.'
	'\nSee the following issue for details: https://github.com/scikit-fmm/scikit-fmm/issues/28'
	)
	return v

And also in the tests:

scikit-mpe/tests/test_mpe.py

Line 13 in 59551ba

pytest.param(2, marks=pytest.mark.skip('https://github.com/scikit-fmm/scikit-fmm/issues/28')),

[jkfurtney]

This should be fixed in scikit-fmm master, can you give it a try and let me know if you find any issues? Thanks

[espdev]

@jkfurtney I have checked my code from refactoring-and-docs branch with scikit-fmm from master. It works fine! All tests with order 1 and 2 were completed successfully.

Thank you!