# Copyright 2021 The QHBM Library Authors. All Rights Reserved.
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# Licensed under the Apache License, Version 2.0 (the "License");
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# https://www.apache.org/licenses/LICENSE-2.0
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# ==============================================================================
"""Implementation of the QMHL loss function."""
from qhbmlib.data import quantum_data
from qhbmlib.inference import qhbm
[docs]def qmhl(data: quantum_data.QuantumData, input_qhbm: qhbm.QHBM):
"""Calculate the QMHL loss of the QHBM against the quantum data.
See equation 21 in the appendix.
Args:
data: The data mixed state to learn.
input_qhbm: QHBM being trained to approximate `data`.
Returns:
The quantum cross-entropy between the data and the model.
"""
return (data.expectation(input_qhbm.modular_hamiltonian) +
input_qhbm.e_inference.log_partition())