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I am trying to run the following circuit:

from qiskit.circuit import ParameterVector, QuantumCircuit
p = qiskit.circuit.ParameterVector('p', 2)
th = qiskit.circuit.ParameterVector('th', 2)

circuit = qiskit.circuit.QuantumCircuit(2)
circuit.rx(p[0], 0) 
circuit.ry(p[1], 1)
circuit.ry(th[1], 1)
circuit.ry(th[0], 1)

qc = transpile(circuit, backend)

I want to pass parameters from two different lists, inp[0] and theta, each of length 2, like so:

bind_dict = {}
j = 0
for key in qc.parameters:
    while j <= 1: #this is the number of inputs, at the moment we have two inputs
        bind_dict[key] = inp[0][j]
        j+=1
    k = 0
    bind_dict[key] = theta[k]

qc.assign_parameters(bind_dict)
qobj = assemble(qc, shots = 10)

I get the following error:

Traceback (most recent call last):
  Input In [316] in <cell line: 1>
    qobj = assemble(qc, shots = 10)
  File /opt/conda/lib/python3.8/site-packages/qiskit/compiler/assembler.py:205 in assemble
    bound_experiments, run_config = _expand_parameters(
  File /opt/conda/lib/python3.8/site-packages/qiskit/compiler/assembler.py:596 in _expand_parameters
    raise QiskitError(
QiskitError: 'Mismatch between run_config.parameter_binds and all circuit parameters.
Parameter binds: [] Circuit parameters: [ParameterView([ParameterVectorElement(p[0]),     
ParameterVectorElement(p[1]), ParameterVectorElement(th[0]),   
ParameterVectorElement(th[1])])]'

Use %tb to get the full traceback.

It does not seem to assign the parameters to the circuit?

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1 Answer 1

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By default, QuantumCircuit.assign_parameters() will return a copy of the circuit with the bound parameters. The circuit instance itself will not be modified. To modify it you will need to call it as follows:

qc.assign_parameters(bind_dict, inplace = True)
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3
  • $\begingroup$ Thank you for the reply, unfortunately even with this modification, I still get the same error. Could it be something else? $\endgroup$
    – Cat Telliber
    May 27, 2022 at 15:22
  • $\begingroup$ I tested your code on my machine. It works after this modification. $\endgroup$
    – Egretta.Thula
    May 27, 2022 at 15:27
  • $\begingroup$ You're right, I don't know why it didn't work for me at first but after restarting the kernel it works. Thanks a lot!! $\endgroup$
    – Cat Telliber
    May 27, 2022 at 15:40

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