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Parameter

Parameter(name) GitHub(opens in a new tab)

Bases: qiskit.circuit.parameterexpression.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.bind_parameters({phi: 3.14})
bc.measure_all()
bc.draw('mpl')

(Source code)

../_images/qiskit-circuit-Parameter-1_00.png

Fig. 10 (png, hires.png, pdf)

../_images/qiskit-circuit-Parameter-1_01.png

Fig. 11 (png, hires.png, pdf)

Create a new named Parameter.

Parameters

name (str) – name of the Parameter, used for visual representation. This can be any unicode string, e.g. “ϕ”.


Methods

arccos

Parameter.arccos()

Arccos of a ParameterExpression

arcsin

Parameter.arcsin()

Arcsin of a ParameterExpression

arctan

Parameter.arctan()

Arctan of a ParameterExpression

assign

Parameter.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 (Union[ParameterExpression, float]) – The new value to bind to.

Return type

ParameterExpression

Returns

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

bind

Parameter.bind(parameter_values, allow_unknown_parameters=False)

Binds the provided set of parameters to their corresponding values.

Parameters

  • parameter_values (Dict) – Mapping of Parameter instances to the numeric value to which they will be bound.
  • allow_unknown_parameters (bool) – 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

  • CircuitError

    • If parameter_values contains Parameters outside those in self. - If a non-numeric value is passed in parameter_values.
  • ZeroDivisionError

    • If binding the provided values requires division by zero.

Return type

ParameterExpression

Returns

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

conjugate

Parameter.conjugate()

Return the conjugate.

Return type

ParameterExpression

cos

Parameter.cos()

Cosine of a ParameterExpression

exp

Parameter.exp()

Exponential of a ParameterExpression

gradient

Parameter.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

Return type

Union[ParameterExpression, complex]

Returns

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

is_real

Parameter.is_real()

Return whether the expression is real

log

Parameter.log()

Logarithm of a ParameterExpression

sin

Parameter.sin()

Sine of a ParameterExpression

subs

Parameter.subs(parameter_map, allow_unknown_parameters=False)

Substitute self with the corresponding parameter in parameter_map.

sympify

Parameter.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

Parameter.tan()

Tangent of a ParameterExpression


Attributes

name

Returns the name of the Parameter.

parameters

Returns a set of the unbound Parameters in the expression.

Return type

Set

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