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Fix random seed initialization between runs in SabreSwap #9127

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merged 2 commits into from
Nov 15, 2022
+14 −9
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Fix random seed initialization between runs in SabreSwap #9127

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e1b42b0
Fix random seed initialization between runs in SabreSwap
mtreinish Nov 14, 2022
7ba9700
Remove unused numpy import
mtreinish Nov 15, 2022
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8 changes: 1 addition & 7 deletions qiskit/transpiler/passes/routing/sabre_swap.py
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,6 @@
import logging
from copy import copy, deepcopy

import numpy as np
import retworkx

from qiskit.circuit.library.standard_gates import SwapGate
Expand Down Expand Up @@ -150,12 +149,7 @@ def __init__(self, coupling_map, heuristic="basic", seed=None, fake_run=False, t
self._neighbor_table = NeighborTable(retworkx.adjacency_matrix(self.coupling_map.graph))

self.heuristic = heuristic

if seed is None:
ii32 = np.iinfo(np.int32)
self.seed = np.random.default_rng(None).integers(0, ii32.max, dtype=int)
else:
self.seed = seed
self.seed = seed
if trials is None:
self.trials = CPU_COUNT
else:
Expand Down
8 changes: 8 additions & 0 deletions releasenotes/notes/fix-sabre-swap-random-seed-dcf3dace63042791.yaml
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@@ -0,0 +1,8 @@
---
fixes:
- |
Fixed an issue with the :class:`~.SabreSwap` pass which would cause the
output of multiple runs of the pass without the ``seed`` argument specified
to reuse the same random number generator seed between runs instead of
using different seeds. This previously caused identical results to be
returned between runs even when no ``seed`` was specified.
7 changes: 5 additions & 2 deletions src/sabre_swap/mod.rs
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Expand Up @@ -152,14 +152,17 @@ pub fn build_swap_map(
neighbor_table: &NeighborTable,
distance_matrix: PyReadonlyArray2<f64>,
heuristic: &Heuristic,
seed: u64,
seed: Option<u64>,
layout: &mut NLayout,
num_trials: usize,
) -> (SwapMap, PyObject) {
let run_in_parallel = getenv_use_multiple_threads() && num_trials > 1;
let dist = distance_matrix.as_array();
let coupling_graph: DiGraph<(), ()> = cmap_from_neighor_table(neighbor_table);
let outer_rng = Pcg64Mcg::seed_from_u64(seed);
let outer_rng = match seed {
Some(seed) => Pcg64Mcg::seed_from_u64(seed),
None => Pcg64Mcg::from_entropy(),
};
let seed_vec: Vec<u64> = outer_rng
.sample_iter(&rand::distributions::Standard)
.take(num_trials)
Expand Down