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Dashboard Core — System Limits

Real, per-machine qubit limits — detects actual available RAM instead of a number picked to fit whatever machine this was developed on, so Composer refuses an allocation that would actually exhaust memory rather than crashing partway through.

from dashboard_core.system_limits import max_safe_dense_qubits

limits = max_safe_dense_qubits()
print(limits)
# {'total_mb': 8066.7, 'available_mb': 3039.0, 'threshold_pct': 0.15, 'max_qubits_dense': 27}
# (total_mb/available_mb/max_qubits_dense are real, machine-dependent values --
#  this is one real run's output, not a fixed constant; max_qubits_dense is
#  always between 16 and 27)

system_limits

Real, per-machine qubit limits -- detects actual available RAM instead of a number picked to fit whatever machine this was developed on. A modest 8 GB dev laptop and a 128 GB workstation get genuinely different limits.

Reuses dense_evolution.chunk.get_dynamic_chunk, the same real, already-tested RAM-based sizing function the Chunk engine itself uses (confirmed in feature/streamlit-dashboard's older simulation_runner.py: "Decided by de.Chunk's own dynamic, available-RAM-based sizing... not a hardcoded qubit-count constant, so it adapts to the machine it's running on") -- rather than a second, slightly different hand-rolled formula. The actual safety enforcement (rejecting a request that would genuinely overflow RAM) is separate: dashboard_core.engine.run_circuit_from_qasm calls dense_evolution.chunk.SafeMemoryGuard.check_allocation directly, which has no floor -- this module is only the UI's suggested/default cap.

max_safe_dense_qubits 

max_safe_dense_qubits() -> dict

Suggested max qubit count for the Composer's Qubits field, from dense_evolution.chunk.get_dynamic_chunk(complex128) -- floor 16, ceiling 30 by that function's own design (a chunk always has some minimum useful size, and 30 qubits/~17 GB is its own practical ceiling for a single dense block -- raised from 27 in Dense-Evolution PR #278, which was discarding real headroom on any 16GB+ GPU). MPS's contract_to_statevector has a separate, RAM-independent hard ceiling of 24 qubits; picking 25-30 with the MPS backend surfaces that function's own real error rather than being silently blocked here.

Returns:

Type Description
dict

total_mb/available_mb (this machine's real RAM, from SafeMemoryGuard.status()), threshold_pct (the guard's safety margin), max_qubits_dense (the suggested cap -- machine-dependent, not a constant).

Examples:

>>> from dashboard_core.system_limits import max_safe_dense_qubits
>>> limits = max_safe_dense_qubits()
>>> sorted(limits.keys())
['available_mb', 'max_qubits_dense', 'threshold_pct', 'total_mb']
>>> 16 <= limits['max_qubits_dense'] <= 30
True
Source code in tools/dashboard/core/system_limits.py 
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def max_safe_dense_qubits() -> dict:
    """Suggested max qubit count for the Composer's Qubits field, from
    dense_evolution.chunk.get_dynamic_chunk(complex128) -- floor 16,
    ceiling 30 by that function's own design (a chunk always has *some*
    minimum useful size, and 30 qubits/~17 GB is its own practical ceiling
    for a single dense block -- raised from 27 in Dense-Evolution PR #278,
    which was discarding real headroom on any 16GB+ GPU). MPS's
    contract_to_statevector has a separate, RAM-independent hard ceiling
    of 24 qubits; picking 25-30 with the MPS backend surfaces that
    function's own real error rather than being silently blocked here.

    Returns
    -------
    dict
        `total_mb`/`available_mb` (this machine's real RAM, from
        `SafeMemoryGuard.status()`), `threshold_pct` (the guard's safety
        margin), `max_qubits_dense` (the suggested cap -- machine-dependent,
        not a constant).

    Examples
    --------
    >>> from dashboard_core.system_limits import max_safe_dense_qubits
    >>> limits = max_safe_dense_qubits()
    >>> sorted(limits.keys())
    ['available_mb', 'max_qubits_dense', 'threshold_pct', 'total_mb']
    >>> 16 <= limits['max_qubits_dense'] <= 30
    True
    """
    guard = de.chunk.SafeMemoryGuard()
    status = guard.status()
    max_qubits = de.chunk.get_dynamic_chunk(de.chunk.jnp.complex128 if de.chunk.HAS_JAX else de.chunk.np.complex128)

    return {
        "total_mb": status["total_mb"],
        "available_mb": status["available_mb"],
        "threshold_pct": guard.threshold_pct,
        "max_qubits_dense": max_qubits,
    }