access the objective function during optimisation

[poutine-dejeuner]

From the meepcon2022 tutorial notebook, there is a cell in which the optimisation problem is set up. The objective function J is defined. How can I access the value of the objective function J? More generally, I am interested in how to reproduce the same eigenmode computation from a simulation object directly.

`TE0 = mpa.EigenmodeCoefficient(sim,
mp.Volume(center=mp.Vector3(x=-Sx/2 + pml_size + 2waveguide_length/3),
size=mp.Vector3(y=1.5)),mode)
TE_top = mpa.EigenmodeCoefficient(sim,
mp.Volume(center=mp.Vector3(Sx/2 - pml_size - 2waveguide_length/3,arm_separation/2,0),
size=mp.Vector3(y=arm_separation)),mode)
TE_bottom = mpa.EigenmodeCoefficient(sim,
mp.Volume(center=mp.Vector3(Sx/2 - pml_size - 2*waveguide_length/3,-arm_separation/2,0),
size=mp.Vector3(y=arm_separation)),mode)
ob_list = [TE0,TE_top,TE_bottom]

def J(source,top,bottom):
power = npa.abs(top/source) ** 2 + npa.abs(bottom/source) ** 2
return npa.mean(power)

opt = mpa.OptimizationProblem(
simulation = sim,
objective_functions = J,
objective_arguments = ob_list,
design_regions = [design_region],
frequencies=frequencies`