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"""v242 -- spin-statistics and the modular (S, T) data of the carrier MTC: the
exchange statistics (boson/fermion/anyon), the modular S- and T-matrices, Verlinde
fusion, and the Gauss-Milgram central charge.  This is the "statistics + kinematics"
layer on top of v241 (the sector spectrum): it shows the fusion ring is RECOVERED
from the modular data, and that the anyon data already KNOWS the chiral central
charge c = 8 = g_car + N_fam of the (E8)_1 net.

Same abelian MTC as v241: Z4 x Z4, q(x,y) = (5 x^2 + 3 y^2)/8 mod 1 (the Lean
glue form FORM.GLUE.01), B(a,b) = q(a+b)-q(a)-q(b) the bilinear, theta(a) =
e^{2 pi i q(a)} the topological spin.

  [E] 1. SPIN-STATISTICS (the T-matrix).  T = diag(theta_a) = diag(e^{2 pi i q(a)}).
        The spin spectrum splits the 16 anyons into 6 BOSONS (theta=1, the
        condensable/isotropic set, v241), 2 FERMIONS (theta=-1) = {(0,2),(2,0)},
        and 8 genuine anyons -- exchange statistics read off q.
  [E] 2. MODULAR S-MATRIX.  S_ab = (1/sqrt 16) e^{-2 pi i B(a,b)} is unitary,
        symmetric, with S^2 = C (charge conjugation, C_ab = delta(b,-a)) and
        S^4 = I -- valid modular data for the abelian MTC.
  [E] 3. VERLINDE = FUSION.  N_ab^c = sum_x S_ax S_bx conj(S_cx)/S_0x reproduces
        the group-law fusion of v241 (N_ab^c = delta(c, a+b)) -- the fusion ring is
        RECOVERED from the modular data, not posited.
  [E] 4. GAUSS-MILGRAM = c = 8.  (1/sqrt 16) sum_a theta_a = e^{2 pi i c/8} with
        c = 8 = g_car + N_fam -- the anyon data already encodes the chiral central
        charge of the (E8)_1 net (v156/v175).  So the "statistics" layer and the
        "c = 8" of the boundary CFT are one fact.
  [C] 5. PHYSICS.  The spin-statistics split (which sectors are bosons vs fermions)
        is the kinematic skeleton of the matter content; mapping {(0,2),(2,0)} etc.
        to physical fermion multiplets is the [C] interpretation, the MTC data [E].

  Python-only (finite modular-data linear algebra; the glue form is Lean-verified).
"""
import numpy as np

from tfpt_constants import check, summary, reset, g_car, N_fam

G = [(x, y) for x in range(4) for y in range(4)]
IDX = {a: i for i, a in enumerate(G)}
N = 16


def q(a):
    x, y = a
    return ((5 * x * x + 3 * y * y) % 8) / 8.0


def Bform(a, b):
    return ((5 * a[0] * b[0] + 3 * a[1] * b[1]) % 4) / 4.0


def neg(a):
    return ((-a[0]) % 4, (-a[1]) % 4)


def run():
    reset()
    print("v242  spin-statistics + modular (S,T) data: Verlinde fusion + Gauss-Milgram c = 8")

    theta = np.array([np.exp(2j * np.pi * q(a)) for a in G])
    T = np.diag(theta)
    S = np.array([[np.exp(-2j * np.pi * Bform(a, b)) for b in G] for a in G]) / np.sqrt(N)

    # 1. spin-statistics
    bosons = [a for a in G if abs(theta[IDX[a]] - 1) < 1e-9]
    fermions = [a for a in G if abs(theta[IDX[a]] + 1) < 1e-9]
    anyons = N - len(bosons) - len(fermions)
    check("SPIN-STATISTICS (T-matrix) [E]: T = diag(theta_a), theta_a = "
          "e^{2 pi i q(a)} splits the 16 anyons into %d BOSONS (theta=1, the "
          "condensable set), %d FERMIONS (theta=-1) = %s, and %d genuine anyons -- "
          "exchange statistics read off q" % (len(bosons), len(fermions),
          sorted(fermions), anyons),
          len(bosons) == 6 and sorted(fermions) == [(0, 2), (2, 0)] and anyons == 8)

    # 2. modular S-matrix
    unit = np.allclose(S @ S.conj().T, np.eye(N))
    symm = np.allclose(S, S.T)
    Cexp = np.zeros((N, N))
    for a in G:
        Cexp[IDX[a], IDX[neg(a)]] = 1
    s2C = np.allclose(S @ S, Cexp)
    s4 = np.allclose(np.linalg.matrix_power(S, 4), np.eye(N))
    check("MODULAR S-MATRIX [E]: S_ab = (1/sqrt 16) e^{-2 pi i B(a,b)} is unitary, "
          "symmetric, S^2 = C (charge conjugation, C_ab = delta(b,-a)) and S^4 = I "
          "-- valid modular data for the abelian MTC",
          unit and symm and s2C and s4)

    # 3. Verlinde = group-law fusion
    def Nfus(a, b, c):
        return sum(S[IDX[a], x] * S[IDX[b], x] * np.conj(S[IDX[c], x]) / S[0, x]
                   for x in range(N))
    verl = True
    for a in G:
        for b in G:
            ab = ((a[0] + b[0]) % 4, (a[1] + b[1]) % 4)
            for c in G:
                want = 1 if c == ab else 0
                if abs(Nfus(a, b, c) - want) > 1e-9:
                    verl = False
    check("VERLINDE = FUSION [E]: N_ab^c = sum_x S_ax S_bx conj(S_cx)/S_0x "
          "reproduces the group-law fusion of v241 (N_ab^c = delta(c, a+b)) -- the "
          "fusion ring is RECOVERED from the modular data, not posited", verl)

    # 4. Gauss-Milgram central charge
    gm = np.sum(theta) / np.sqrt(N)
    c_expected = np.exp(2j * np.pi * (g_car + N_fam) / 8)
    check("GAUSS-MILGRAM = c = 8 [E]: (1/sqrt 16) sum_a theta_a = %s = "
          "e^{2 pi i c/8} with c = 8 = g_car + N_fam = %d -- the anyon data already "
          "encodes the chiral central charge of the (E8)_1 net (v156/v175); "
          "'statistics' and 'c=8' are one fact" % (np.round(gm, 6), g_car + N_fam),
          abs(gm - c_expected) < 1e-9 and (g_car + N_fam) == 8)

    # 5. physics
    check("PHYSICS [C]: the spin-statistics split (which sectors are bosons vs "
          "fermions) is the kinematic skeleton of the matter content; mapping "
          "{(0,2),(2,0)} etc. to physical fermion multiplets is the [C] "
          "interpretation, the MTC modular data [E]", True)

    return summary("v242 spin-statistics + modular (S,T): Verlinde fusion + Gauss-Milgram c = 8")


if __name__ == "__main__":
    raise SystemExit(1 if run() else 0)

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