Error when optimizing over goos.Cuboid variable.

[ichristen]

Hi,

First of all, thanks to all of you for making this codebase open-source. It really is awesome to not have to go about reinventing this particular wheel.

I am interested in optimizing grating efficiency over the z-position of a reflective buried layer (in addition to a standard barcode grating optimization). I attempted to do this by inserting a 3-vector goos.Variable into the goos.Cuboid that is the reflective buried layer. However, when running the simulation, I receive errors similar to ValueError: 0-th dimension must be fixed to 489 but got 487. After some digging, I determined that a 3-vector from my variable is appended to the initial_val list (as expected), whereas the grad(x) list is given a 1-vector from my variable (see spins/goos/optimize.py:run()). Hence the error, as scipy.optimize.minimize gets confused when trying to apply a N+1-long Jacobian to a N+3-long vector. At this point, I wasn't sure if goos.Cuboids hadn't been fully-implemented in goos or if I was using something incorrectly, so I would appreciate any insight. It is possible that I'm initializing the goos.Variable incorrectly or something.

One can test out this issue easily by editing a line or two in the substrate variable from the examples/goos/grating_1d example (in this example, the z-position of the substrate isn't super critical for grating optimization, but it illustrates the issue). The different variants that I tried included:

• Original code (works):

substrate = goos.Cuboid(
    pos=goos.Constant([
        params.coupler_len / 2, 0,
        -params.box_size - params.wg_thickness / 2 - 5000
    ]),
    extents=goos.Constant([params.coupler_len + 10000, 1000, 10000]),
    material=goos.material.Material(index=params.eps_wg))

• Turning extents into a 3-vector goos.Variable (fails):

substrate = goos.Cuboid(
    pos=goos.Constant([
        params.coupler_len / 2, 0,
        -params.box_size - params.wg_thickness / 2 - 5000
    ]),
    extents=goos.Variable([params.coupler_len + 10000, 1000, 10000]),
    material=goos.material.Material(index=params.eps_wg))

• Adding a 3-vector goos.Variable to extents (fails):

substrate = goos.Cuboid(
    pos=goos.Constant([
        params.coupler_len / 2, 0,
        -params.box_size - params.wg_thickness / 2 - 5000
    ]),
    extents=goos.Constant([params.coupler_len + 10000, 1000, 10000]) + goos.Variable([0, 0, 0]),
    material=goos.material.Material(index=params.eps_wg))

• Multiplying extents by a 1-vector goos.Variable (fails):

substrate = goos.Cuboid(
    pos=goos.Constant([
        params.coupler_len / 2, 0,
        -params.box_size - params.wg_thickness / 2 - 5000
    ]),
    extents=goos.Variable(1) * goos.Constant([params.coupler_len + 10000, 1000, 10000]),
    material=goos.material.Material(index=params.eps_wg))

• Variations of the above with upper and lower bounds included on the goos.Variable (fails).
• Variations of the above that try to change pos rather than extents [although the code of goos.CuboidFlow seems to imply that one should make extents that goos.Variable, not pos?] (fails).

Thanks much for any help!

[JesseLu]

Hi! Is this still an issue?

[JesseLu]

Closing for now.