mps基础脚本

baseline_mps_expectation.py

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+"""Baseline MPS expectation scan with the qmatchatea backend."""
+
+import argparse
+import logging
+import math
+import time
+
+from qibo import Circuit, gates, hamiltonians
+from qibo.symbols import X, Z
+
+from qibotn.backends.qmatchatea import QMatchaTeaBackend
+
+
+def parse_bonds(value):
+    return [int(item) for item in value.split(",") if item.strip()]
+
+
+def build_circuit(nqubits, nlayers, seed):
+    import numpy as np
+
+    rng = np.random.default_rng(seed)
+    circuit = Circuit(nqubits)
+    for _ in range(nlayers):
+        for qubit in range(nqubits):
+            circuit.add(gates.RY(qubit, theta=rng.uniform(-math.pi, math.pi)))
+            circuit.add(gates.RZ(qubit, theta=rng.uniform(-math.pi, math.pi)))
+        for qubit in range(0, nqubits - 1, 2):
+            circuit.add(gates.CNOT(qubit, qubit + 1))
+        for qubit in range(1, nqubits - 1, 2):
+            circuit.add(gates.CNOT(qubit, qubit + 1))
+    return circuit
+
+
+def build_observable(nqubits):
+    form = 0
+    for qubit in range(nqubits - 1):
+        form += 0.5 * Z(qubit) * Z(qubit + 1)
+    form += 0.25 * X(0)
+    return hamiltonians.SymbolicHamiltonian(form=form)
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--nqubits", type=int, default=20)
+    parser.add_argument("--nlayers", type=int, default=8)
+    parser.add_argument("--bonds", type=parse_bonds, default=parse_bonds("2,4,8,16,32"))
+    parser.add_argument("--seed", type=int, default=42)
+    parser.add_argument("--cut-ratio", type=float, default=1e-12)
+    parser.add_argument("--svd-control", default="V")
+    parser.add_argument("--no-exact", action="store_true")
+    args = parser.parse_args()
+    logging.getLogger("qibo.config").setLevel(logging.ERROR)
+    logging.getLogger("qtealeaves").setLevel(logging.ERROR)
+
+    circuit = build_circuit(args.nqubits, args.nlayers, args.seed)
+    observable = build_observable(args.nqubits)
+    exact = None
+    if not args.no_exact:
+        exact = float(observable.expectation_from_state(circuit().state()).real)
+
+    print(f"nqubits={args.nqubits} nlayers={args.nlayers} seed={args.seed}")
+    if exact is not None:
+        print(f"exact={exact:.16e}")
+    print("bond_dim expval abs_error rel_error seconds")
+
+    backend = QMatchaTeaBackend()
+    for bond in args.bonds:
+        backend.configure_tn_simulation(
+            ansatz="MPS",
+            max_bond_dimension=bond,
+            cut_ratio=args.cut_ratio,
+            svd_control=args.svd_control,
+        )
+        start = time.perf_counter()
+        value = float(backend.expectation(circuit, observable, preprocess=False).real)
+        elapsed = time.perf_counter() - start
+        abs_error = float("nan") if exact is None else abs(value - exact)
+        rel_error = float("nan") if exact is None else abs_error / max(abs(exact), 1e-15)
+        print(f"{bond:d} {value:.16e} {abs_error:.6e} {rel_error:.6e} {elapsed:.3f}")
+
+
+if __name__ == "__main__":
+    main()