`init_ghosted` gives rounding errors on domain boundary

[EmilyBourne]

`init_ghosted` gives rounding errors on domain boundary

[tpadioleau]

It is true that you cannot expect exact equality between vx_min and ddc::coordinate(main_domain.front())/vx_xmax and ddc::coordinate(main_domain.back()). I don't think it is related to init_ghosted though, I guess init also has the same behavior. Are you relying on it in Gysela ?

[EmilyBourne]

I guess init also has the same behavior

I think for init you cannot expect exact equality between vx_xmax and ddc::coordinate(main_domain.back()) but you can expect exact equality between vx_xmin and ddc::coordinate(main_domain.front())

We are not relying on this for Gysela, but in DDC you were relying on it here:

ddc/include/ddc/kernels/splines/bsplines_uniform.hpp

Lines 557 to 558 in 0da9a03

	assert(x - rmin() >= -length() * 1e-14);
	assert(rmax() - x >= -length() * 1e-14);

if the extrapolation condition for a spline evaluator evaluates the value at the boundary.

As I say in the issue

it may not be serious, but it should at least be documented so users are aware of this potential pitfall.