SurfaceRZFourier cache isn't invalidated by setting rc, zs, rs, zc arrays

[missing-user]

There are not setter properties for the variables rc, zs, rs, zc, so recompute_bell() is not triggered by overwriting them.

For example, this means that plots, or depending objective functions aren't updated when overwriting the entire rc array, e.g. to scale a configuration by a constant factor. The following example script will plot the same torus twice, eventho the coefficients were changed (same problem with ).

from simsopt import geo
import matplotlib.pyplot as plt
s = geo.SurfaceRZFourier(3, True, 5, 8)
s.make_rotating_ellipse(1, .2, .5, .1)
s.plot()
plt.show()
scaling = 10
s.rc = s.rc * scaling # This doesn't invalidate the cache
s.zc *= scaling         # or equivalently
s.plot()
plt.show()

can now be done with

from simsopt import geo
import matplotlib.pyplot as plt
s = geo.SurfaceRZFourier(3, True, 5, 8)
s.make_rotating_ellipse(1, .2, .5, .1)
s.plot()
plt.show()
scaling = 10
s.rc_array = s.rc * scaling
s.zc_array *= scaling
s.plot()
plt.show()

My suggestion is to either

• Add array setter properties to the fourier components of the surface (this PR)
• Refactor SurfaceRZFourier to have private _rc and property decorators for the accessors rc, but that would also involve changing the CPP class and seems quite invasive
• Add a short warning to the set_zs() docstring:
  """Modifyting the zs array directly is discouraged, since it doesn't trigger the recompute_bell(). """