# Author: Alex Gezerlis

# Numerical Methods in Physics with Python (CUP, 2020)

from qrmet import qrmet

from kron import paulimatrices, kron

import numpy as np

def threespins(omI,omII,omIII,gam):

hbar = 1.

paulis = paulimatrices()

iden = np.identity(2)

SIs = [hbar*kron(kron(pa,iden),iden)/2 for pa in paulis]

SIIs = [hbar*kron(kron(iden,pa),iden)/2 for pa in paulis]

SIIIs = [hbar*kron(kron(iden,iden),pa)/2 for pa in paulis]

SIdotII = sum([SIs[i]@SIIs[i] for i in range(3)])

SIdotIII = sum([SIs[i]@SIIIs[i] for i in range(3)])

SIIdotIII = sum([SIIs[i]@SIIIs[i] for i in range(3)])

H = -omI*SIs[2] - omII*SIIs[2] - omIII*SIIIs[2]

H += gam*(SIdotII+SIdotIII+SIIdotIII)

H = H.real

return H

if __name__ == '__main__':

np.set_printoptions(precision=3)

H = threespins(1.,2.,3.,0.5)

qreigvals = qrmet(H); print(qreigvals)