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11 changes: 8 additions & 3 deletions torchquantum/algorithm/hamiltonian.py
Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,7 @@
import torchquantum.functional as tqf
import numpy as np

from typing import Any, Iterable, List
from typing import Any, Iterable, List, Union
from torchquantum.util import pauli_string_to_matrix

__all__ = ["Hamiltonian"]
Expand Down Expand Up @@ -96,6 +96,7 @@ def __init__(self,
coeffs: List[float],
paulis: List[str],
endianness: str = "big",
device: Union[torch.device, str, None] = None
) -> None:
"""Initialize the Hamiltonian.
Args:
Expand Down Expand Up @@ -125,6 +126,8 @@ def __init__(self,
self.coeffs = coeffs
self.paulis = paulis
self.endianness = endianness
self.dev = (torch.device(device) if isinstance(device, str)
else device)
if self.endianness == "little":
self.paulis = [pauli[::-1] for pauli in self.paulis]

Expand All @@ -135,9 +138,11 @@ def matrix(self) -> torch.Tensor:

def get_matrix(self) -> torch.Tensor:
"""Return the matrix of the Hamiltonian."""
matrix = self.coeffs[0] * pauli_string_to_matrix(self.paulis[0])
matrix = self.coeffs[0] * pauli_string_to_matrix(self.paulis[0],
device=self.dev)
for coeff, pauli in zip(self.coeffs[1:], self.paulis[1:]):
matrix += coeff * pauli_string_to_matrix(pauli)
matrix += coeff * pauli_string_to_matrix(pauli,
device=self.dev)

return matrix

Expand Down
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