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classical_proposal

qemcmc.sampler.classical_proposal

ClassicalProposal 

ClassicalProposal(model, method='uniform')

Bases: Proposal

Classical Markov Chain Monte Carlo proposer.

This class implements purely classical proposal mechanisms for MCMC. New candidate states are generated either by sampling a completely random (uniform) configuration, or by performing a local single-spin or two-spin flip.

Parameters:

Name Type Description Default
model EnergyModel

Energy model defining the target Boltzmann distribution.

 required
method str

Proposal mechanism used to generate candidate states.

  • "uniform" : propose a completely random spin configuration.
  • "local" : flip a single randomly chosen spin.
  • "2-local" : flip two randomly chosen spins.

Default is "uniform".

 'uniform'
Source code in src/qemcmc/sampler/classical_proposal.py 
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def __init__(self, model: EnergyModel, method: str = "uniform"):
    if method not in self.METHODS:
        raise ValueError(f"Method '{method}' is not supported. Choose from 'uniform', 'local', or '2-local'.")
    super().__init__(model)
    self.method = method

update_uniform 

update_uniform(current_state_bitstring)

Proposes a new state by generating a random bitstring.

Parameters:

Name Type Description Default
current_state_bitstring str

The current state represented as a bitstring (not used, but required by the API).

 required

Returns:

Type Description
str

A new random state bitstring of the same length.
Source code in src/qemcmc/sampler/classical_proposal.py 
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def update_uniform(self, current_state_bitstring: str) -> str:
    """
    Proposes a new state by generating a random bitstring.

    Parameters
    ----------
    current_state_bitstring : str
        The current state represented as a bitstring (not used, but required by the API).

    Returns
    -------
    str
        A new random state bitstring of the same length.
    """

    return get_random_state(len(current_state_bitstring))

update_local 

update_local(current_state_bitstring)

Proposes a new state by flipping a single randomly chosen spin.

Parameters:

Name Type Description Default
current_state_bitstring str

The current state represented as a bitstring.

 required

Returns:

Type Description
str

The new state bitstring after flipping one spin.
Source code in src/qemcmc/sampler/classical_proposal.py 
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def update_local(self, current_state_bitstring: str) -> str:
    """
    Proposes a new state by flipping a single randomly chosen spin.

    Parameters
    ----------
    current_state_bitstring : str
        The current state represented as a bitstring.

    Returns
    -------
    str
        The new state bitstring after flipping one spin.
    """

    # Randomly choose which spin to flip
    choice = np.random.randint(0, self.n_spins)

    # Flip the chosen spin
    c_s = list(current_state_bitstring)
    c_s[choice] = str(int(c_s[choice]) ^ 1)

    # Return the new state as a bitstring
    return "".join(c_s)

update_2local 

update_2local(current_state_bitstring)

Proposes a new state by flipping two randomly chosen spins.

Parameters:

Name Type Description Default
current_state_bitstring str

The current state represented as a bitstring.

 required

Returns:

Type Description
str

The new state bitstring after flipping two spins.
Source code in src/qemcmc/sampler/classical_proposal.py 
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def update_2local(self, current_state_bitstring: str) -> str:
    """
    Proposes a new state by flipping two randomly chosen spins.

    Parameters
    ----------
    current_state_bitstring : str
        The current state represented as a bitstring.

    Returns
    -------
    str
        The new state bitstring after flipping two spins.
    """
    # Randomly choose which two spins to flip
    choices = np.random.choice(self.n_spins, size=2, replace=False)

    # Flip the chosen spins
    c_s = list(current_state_bitstring)
    for choice in choices:
        c_s[choice] = str(int(c_s[choice]) ^ 1)

    # Return the new state as a bitstring
    return "".join(c_s)