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Parameter

qiskit.circuit.Parameter(name, *, uuid=None) GitHub(opens in a new tab)

Bases: ParameterExpression

Parameter Class for variable parameters.

A parameter is a variable value that is not required to be fixed at circuit definition.

Examples

Construct a variable-rotation X gate using circuit parameters.

from qiskit.circuit import QuantumCircuit, Parameter
 
# create the parameter
phi = Parameter('phi')
qc = QuantumCircuit(1)
 
# parameterize the rotation
qc.rx(phi, 0)
qc.draw('mpl')
 
# bind the parameters after circuit to create a bound circuit
bc = qc.assign_parameters({phi: 3.14})
bc.measure_all()
bc.draw('mpl')
../_images/qiskit-circuit-Parameter-1_00.png../_images/qiskit-circuit-Parameter-1_01.png

Create a new named Parameter.

Parameters

  • name (str(opens in a new tab)) – name of the Parameter, used for visual representation. This can be any unicode string, e.g. “ϕ”.
  • uuid (UUID | None) – For advanced usage only. Override the UUID of this parameter, in order to make it compare equal to some other parameter object. By default, two parameters with the same name do not compare equal to help catch shadowing bugs when two circuits containing the same named parameters are spurious combined. Setting the uuid field when creating two parameters to the same thing (along with the same name) allows them to be equal. This is useful during serialization and deserialization.

Attributes

name

Returns the name of the Parameter.

parameters

Returns a set of the unbound Parameters in the expression.


Methods

abs

abs()

Absolute of a ParameterExpression

arccos

arccos()

Arccos of a ParameterExpression

arcsin

arcsin()

Arcsin of a ParameterExpression

arctan

arctan()

Arctan of a ParameterExpression

assign

assign(parameter, value)

Assign one parameter to a value, which can either be numeric or another parameter expression.

Parameters

  • parameter (Parameter) – A parameter in this expression whose value will be updated.
  • value – The new value to bind to.

Returns

A new expression parameterized by any parameters which were not bound by assignment.

bind

bind(parameter_values, allow_unknown_parameters=False)

Binds the provided set of parameters to their corresponding values.

Parameters

  • parameter_values (dict(opens in a new tab)) – Mapping of Parameter instances to the numeric value to which they will be bound.
  • allow_unknown_parameters (bool(opens in a new tab)) – If False, raises an error if parameter_values contains Parameters in the keys outside those present in the expression. If True, any such parameters are simply ignored.

Raises

Returns

A new expression parameterized by any parameters which were not bound by parameter_values.

Return type

ParameterExpression

conjugate

conjugate()

Return the conjugate.

Return type

ParameterExpression

cos

cos()

Cosine of a ParameterExpression

exp

exp()

Exponential of a ParameterExpression

gradient

gradient(param)

Get the derivative of a parameter expression w.r.t. a specified parameter expression.

Parameters

param (Parameter) – Parameter w.r.t. which we want to take the derivative

Returns

ParameterExpression representing the gradient of param_expr w.r.t. param or complex or float number

Return type

ParameterExpression | complex(opens in a new tab)

is_real

is_real()

Return whether the expression is real

log

log()

Logarithm of a ParameterExpression

sign

sign()

Sign of a ParameterExpression

sin

sin()

Sine of a ParameterExpression

subs

subs(parameter_map, allow_unknown_parameters=False)

Substitute self with the corresponding parameter in parameter_map.

sympify

sympify()

Return symbolic expression as a raw Sympy or Symengine object.

Symengine is used preferentially; if both are available, the result will always be a symengine object. Symengine is a separate library but has integration with Sympy.

Note

This is for interoperability only. Qiskit will not accept or work with raw Sympy or Symegine expressions in its parameters, because they do not contain the tracking information used in circuit-parameter binding and assignment.

tan

tan()

Tangent of a ParameterExpression

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