merged hierarchies interpolations results in spurious values

[nicolasaunai]

Here is a L2 patch of the Pzz component of the ion pressure (it does not matter that's this)

and below are cuts at x=21 obtained different means.

The blue curve is obtained from the interpolator Pizz_i evaluated at (21, yp[106:118]) from a hierarchy made with merged=True,interp="nearest"

Notice the drop at y=11.7.
In green, the real patch data values for that location. Notice there is no drop at 11.7.
In red and orange the same cut but made 1 node left and right to the above cut.
With interp=nearest, one expects the blue curve to somehow be in the middle of the red and orange.
Clearly there is a problem

fig, ax = plt.subplots()
x0 = 21
ax.plot(yp[106:130],Pizz_i(21,yp[106:130]), marker='+', label="merged nearest x=21")
ax.axvline(p[2].patch_datas["Pzz"].y[2])
ax.axvline(p[2].patch_datas["Pzz"].y[-3])
ax.plot(p[2].patch_datas["Pzz"].y[2:-2],p[2].patch_datas["Pzz"].dataset[3,2:-2], label="x=20.9")
ax.plot(p[2].patch_datas["Pzz"].y[2:-2],p[2].patch_datas["Pzz"].dataset[4,2:-2], label="true patch data x=21")
ax.plot(p[2].patch_datas["Pzz"].y[2:-2],p[2].patch_datas["Pzz"].dataset[5,2:-2], label="x=21.1")

ax.legend()

[nicolasaunai]

Ok, plotting the data of the patch aove also gives :

I think the error is that I don't calculate the ghosts of my pressure diag.
However, there is in flat_finest_field_2d :

           # all but 1 ghost nodes are removed in order to limit
           # the overlapping, but to keep enough point to avoid
           # any extrapolation for the interpolator
           needed_points = pdata.ghosts_nbr - 1

It's possible somehow the interpolator keeps the value of the one ghost from the right patch instead of the domain value of the left one.

[nicolasaunai]

we should figure out how to tell the interpolator not to learn from ghost values.