[WIP] Linear-optics Twiss functions#1412
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| float(init.get("disp_py", 0.0)), | ||
| ] | ||
| ) | ||
| tunes = None |
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Two modes are supported:
* **Periodic ring** (``init=None``): the one-turn map is computed from the
current lattice, the Wolski 6D eigendecomposition provides the matched
initial Courant-Snyder / Mais-Ripken Twiss, and the closed-orbit
dispersion is obtained from the periodic equation
:math:`(I - M_{4 \times 4}) D = M[0{:}4, 5]`. Fractional tunes are
extracted from the eigenvalue phases and returned in the ``tunes`` key.
* **Transfer line / linac** (``init`` given): the user supplies initial
uncoupled Courant-Snyder parameters; Twiss is then propagated from the
entrance through the lattice without matching.
ax3l
commented
Apr 20, 2026
| # alpha, phase advance mu, and dispersion along s, plus the fractional tunes | ||
| # for rings. The underlying lattice-level building blocks are available as | ||
| # ``sim.lattice.transfer_map(ref)`` (end-to-end map) and | ||
| # ``sim.lattice.map_trace(ref)`` (per-element cumulative trace). |
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This is useful doc, but a bit ill placed here. Belongs in compute_twiss or other user-facing docs.
ax3l
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Apr 20, 2026
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| def _symplectic_form() -> np.ndarray: | ||
| """Return the 6x6 canonical symplectic form J for ordering | ||
| (x, p_x, y, p_y, t, p_t). | ||
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| J is block-diagonal with three 2x2 blocks ``[[0, 1], [-1, 0]]``. A | ||
| matrix ``A`` is symplectic iff ``A^T J A = J``; the Poisson bracket | ||
| of two phase-space functions f, g satisfies | ||
| ``{f, g} = (grad f)^T J (grad g)``. | ||
| """ | ||
| J = np.zeros((6, 6)) | ||
| for i in range(3): | ||
| J[2 * i, 2 * i + 1] = 1.0 | ||
| J[2 * i + 1, 2 * i] = -1.0 | ||
| return J |
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We have a value for this now in CovarianceMatrix.H and SmallMatrix.H that we can bind.
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Two modes are supported:
init=None): the one-turn map is computed from the current lattice, the Wolski 6D eigendecomposition provides the matched initial Courant-Snyder / Mais-Ripken Twiss, and the closed-orbit dispersion is obtained from the periodic equationtuneskey.initgiven): the user supplies initial uncoupled Courant-Snyder parameters; Twiss is then propagated from the entrance through the lattice without matching.