Parameter

class qiskit.circuit.Parameter(name, *, uuid=None)

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')

(Source code)

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”.

• 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()

Absolute of a ParameterExpression

arccos()

Arccos of a ParameterExpression

arcsin()

Arcsin of a ParameterExpression

arctan()

Arctan of a ParameterExpression

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(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.

Returns:

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

Return type:

ParameterExpression

conjugate()

Return the conjugate.

Return type:

ParameterExpression

cos()

Cosine of a ParameterExpression

exp()

Exponential of a ParameterExpression

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

is_real()

Return whether the expression is real

log()

Logarithm of a ParameterExpression

sign()

Sign of a ParameterExpression

sin()

Sine of a ParameterExpression

subs(parameter_map, allow_unknown_parameters=False)

Substitute self with the corresponding parameter in parameter_map.

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()

Tangent of a ParameterExpression