Manual

The Manual is the reading path through the library: what each object is, how to use it, and where it bites. Every computation here has the same shape: write an observable, build a circuit, propagate the observable through the circuit, measure the result against a state, then validate that the truncation did not decide the answer.

import math
from paulistrings import Circuit, PauliSum

observable = PauliSum.from_strings(
    {"XIII": 0.25, "IXII": 0.25, "IIXI": 0.25, "IIIX": 0.25}, num_qubits=4
)

circuit = Circuit(4)
circuit.rz(math.pi / 8, 0)
circuit.cnot(0, 1)
circuit.h(2)

evolved = observable.propagate(circuit, direction="heisenberg")
print(len(evolved), evolved.expectation("x+").real)

5 0.7309698831278217

from_strings accumulates the observable, the three gates conjugate it in reverse under direction="heisenberg", and expectation reads the result against |++++⟩. Four lines, four chapters: PauliSum.from_strings is Operators, Circuit/rz/cnot/h is Circuits, propagate(..., direction=...) is Engine and propagation, and expectation(...) is Measurements. The four chapters follow that same order.

• Operators — the Pauli sum: how an observable or Hamiltonian is written, stored, inspected and saved.
• Circuits — gates and noise channels, composition, importing from stim, qiskit and task JSON, and why one gate is one truncation point.
• Engine and propagation — the propagate call: direction, truncation, validation, incremental runs, stats and memory, the engine internals, and scaling out over NUMA partitions and MPI ranks.
• Measurements — reading a propagated sum against a product state, a stabilizer state, or another Pauli sum, and which state the label denotes in each direction.

Read the chapters in order once; each assumes the ones before it and does not repeat them. Afterwards, enter by topic from the sidebar: every section is self-contained enough to answer one question, and ends with a pointer to the Library page holding the exact signatures and to an Example that uses the same call at scale.

• Against other tools says whether Pauli propagation is the right method for your problem at all, and names the two places a state-vector or stabilizer simulator is strictly better.
• Library is the signature-and-table reference the Manual cites throughout; it holds no rationale of its own.
• First propagation carries the run above further, into the surviving terms’ identities and a cutoff-sweep validation.