Is CSP Layout always the first algorithm used by qiskit transpiler to map quantum circuit?

Question

I'm using Qiskit transpile with optimization_level=3. I was wondering if CSP layout selector is always the first algorithm tried by Qiskit, also if I set as layout_method='noise_adaptive' or other methods.

If not, how to force the transpiler to use CSP layout selector? I tried with layout_method='csp_layout', but I get the following exception:

qiskit.transpiler.exceptions.TranspilerError: 'Invalid layout method csp_layout.

Answer 1

For Qiskit 0.23 or earlier (qiskit-terra 0.16)

The answer is yes, CSPLayout will run in optimization level 2 or higher, even if a layout_method is provided.

This file constructs the pass manager for optimization level 3: https://github.com/Qiskit/qiskit-terra/blob/master/qiskit/transpiler/preset_passmanagers/level3.py

Currently, the first choice for layout selector is always CSPLayout(coupling_map, call_limit=10000, time_limit=60) and the possible options for layout_method (if CSP layout does not find a solution) are 'trivial', 'dense', 'noise_adaptive', and 'sabre'.

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For Qiskit 0.24 or latter (qiskit-terra 0.17)

With the merge of PR #5495, the answer is it depends. CSPLayout runs in level 2 and 3. If layout_method is provided, then that method will be used.