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Switch position_kinetic_operator to Grid (#44)
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@Strilanc @babbush
Strilanc authored and babbush committed May 23, 2017
1 parent bbe99bb commit 234f4fb
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Showing 2 changed files with 32 additions and 58 deletions.
33 changes: 12 additions & 21 deletions src/fermilib/utils/_jellium.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -258,53 +258,47 @@ def momentum_potential_operator(n_dimensions, grid_length,
return operator


def position_kinetic_operator(n_dimensions, grid_length,
length_scale, spinless=False):
def position_kinetic_operator(grid, spinless=False):
"""Return the kinetic operator in position space second quantization.
Args:
n_dimensions: An int giving the number of dimensions for the model.
grid_length: Int, the number of points in one dimension of the grid.
length_scale: Float, the real space length of a box dimension.
grid (Grid): The discretization to use.
spinless: Bool, whether to use the spinless model or not.
Returns:
operator: An instance of the FermionOperator class.
"""
# Initialize.
n_points = grid_length ** n_dimensions
n_points = grid.num_points()
operator = FermionOperator()
if spinless:
spins = [None]
else:
spins = [0, 1]

# Loop once through all lattice sites.
for grid_indices_a in itertools.product(range(grid_length),
repeat=n_dimensions):
for grid_indices_a in grid.all_points_indices():
coordinates_a = position_vector(
grid_indices_a, grid_length, length_scale)
for grid_indices_b in itertools.product(range(grid_length),
repeat=n_dimensions):
grid_indices_a, grid.length, grid.scale)
for grid_indices_b in grid.all_points_indices():
coordinates_b = position_vector(
grid_indices_b, grid_length, length_scale)
grid_indices_b, grid.length, grid.scale)
differences = coordinates_b - coordinates_a

# Compute coefficient.
coefficient = 0.
for momenta_indices in itertools.product(range(grid_length),
repeat=n_dimensions):
for momenta_indices in grid.all_points_indices():
momenta = momentum_vector(
momenta_indices, grid_length, length_scale)
momenta_indices, grid.length, grid.scale)
if momenta.any():
coefficient += (
numpy.cos(momenta.dot(differences)) *
momenta.dot(momenta) / (2. * float(n_points)))

# Loop over spins and identify interacting orbitals.
for spin in spins:
orbital_a = orbital_id(grid_length, grid_indices_a, spin)
orbital_b = orbital_id(grid_length, grid_indices_b, spin)
orbital_a = orbital_id(grid.length, grid_indices_a, spin)
orbital_b = orbital_id(grid.length, grid_indices_b, spin)

# Add interaction term.
operators = ((orbital_a, 1), (orbital_b, 0))
Expand Down Expand Up @@ -397,10 +391,7 @@ def jellium_model(grid, spinless=False, momentum_space=True):
grid.scale,
spinless)
else:
hamiltonian = position_kinetic_operator(grid.dimensions,
grid.length,
grid.scale,
spinless)
hamiltonian = position_kinetic_operator(grid, spinless)
hamiltonian += position_potential_operator(grid.dimensions,
grid.length,
grid.scale,
Expand Down
57 changes: 20 additions & 37 deletions src/fermilib/utils/_jellium_test.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,6 @@

from __future__ import absolute_import

import itertools
import unittest

import numpy
Expand Down Expand Up @@ -129,15 +128,10 @@ def test_momentum_vector(self):
def test_kinetic_integration(self):

# Compute kinetic energy operator in both momentum and position space.
n_dimensions = 2
grid_length = 2
length_scale = 3.
grid = Grid(dimensions=2, length=2, scale=3.)
spinless = False
momentum_kinetic = momentum_kinetic_operator(
Grid(n_dimensions, grid_length, length_scale),
spinless)
position_kinetic = position_kinetic_operator(
n_dimensions, grid_length, length_scale, spinless)
momentum_kinetic = momentum_kinetic_operator(grid, spinless)
position_kinetic = position_kinetic_operator(grid, spinless)

# Diagonalize and confirm the same energy.
jw_momentum = jordan_wigner(momentum_kinetic)
Expand Down Expand Up @@ -196,22 +190,19 @@ def test_model_integration(self):
def test_coefficients(self):

# Test that the coefficients post-JW transform are as claimed in paper.
n_dimensions = 2
grid_length = 3
length_scale = 2.
grid = Grid(dimensions=2, length=3, scale=2.)
spinless = 1
n_orbitals = grid_length ** n_dimensions
n_orbitals = grid.num_points()
n_qubits = (2 ** (1 - spinless)) * n_orbitals
volume = length_scale ** n_dimensions
volume = grid.volume_scale()

# Kinetic operator.
kinetic = position_kinetic_operator(
n_dimensions, grid_length, length_scale, spinless)
kinetic = position_kinetic_operator(grid, spinless)
qubit_kinetic = jordan_wigner(kinetic)

# Potential operator.
potential = position_potential_operator(
n_dimensions, grid_length, length_scale, spinless)
grid.dimensions, grid.length, grid.scale, spinless)
qubit_potential = jordan_wigner(potential)

# Check identity.
Expand All @@ -221,10 +212,8 @@ def test_coefficients(self):

paper_kinetic_coefficient = 0.
paper_potential_coefficient = 0.
for indices in itertools.product(range(grid_length),
repeat=n_dimensions):
momenta = momentum_vector(
indices, grid_length, length_scale)
for indices in grid.all_points_indices():
momenta = momentum_vector(indices, grid.length, grid.scale)
paper_kinetic_coefficient += float(
n_qubits) * momenta.dot(momenta) / float(4. * n_orbitals)

Expand All @@ -246,10 +235,8 @@ def test_coefficients(self):

paper_kinetic_coefficient = 0.
paper_potential_coefficient = 0.
for indices in itertools.product(range(grid_length),
repeat=n_dimensions):
momenta = momentum_vector(
indices, grid_length, length_scale)
for indices in grid.all_points_indices():
momenta = momentum_vector(indices, grid.length, grid.scale)
paper_kinetic_coefficient -= momenta.dot(
momenta) / float(4. * n_orbitals)

Expand All @@ -269,27 +256,25 @@ def test_coefficients(self):
else:
spins = [0, 1]

for indices_a in itertools.product(range(grid_length),
repeat=n_dimensions):
for indices_b in itertools.product(range(grid_length),
repeat=n_dimensions):
for indices_a in grid.all_points_indices():
for indices_b in grid.all_points_indices():

paper_kinetic_coefficient = 0.
paper_potential_coefficient = 0.

position_a = position_vector(
indices_a, grid_length, length_scale)
indices_a, grid.length, grid.scale)
position_b = position_vector(
indices_b, grid_length, length_scale)
indices_b, grid.length, grid.scale)
differences = position_b - position_a

for spin_a in spins:
for spin_b in spins:

p = orbital_id(
grid_length, indices_a, spin_a)
grid.length, indices_a, spin_a)
q = orbital_id(
grid_length, indices_b, spin_b)
grid.length, indices_b, spin_b)

if p == q:
continue
Expand All @@ -300,11 +285,9 @@ def test_coefficients(self):
else:
potential_coefficient = 0.

for indices_c in \
itertools.product(range(grid_length),
repeat=n_dimensions):
for indices_c in grid.all_points_indices():
momenta = momentum_vector(
indices_c, grid_length, length_scale)
indices_c, grid.length, grid.scale)

if momenta.any():
potential_contribution = numpy.pi * numpy.cos(
Expand Down

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