ParameterExpression

class qiskit.circuit.ParameterExpression(symbol_map, expr)

Bases: object

ParameterExpression class to enable creating expressions of Parameters.

Create a new ParameterExpression.

Not intended to be called directly, but to be instantiated via operations on other Parameter or ParameterExpression objects.

Parameters:

• symbol_map (Dict[Parameter, [ParameterExpression, float, or int]]) – Mapping of Parameter instances to the sympy.Symbol serving as their placeholder in expr.

• expr (sympy.Expr) – Expression of sympy.Symbol s.

Attributes

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 (ParameterExpression | float) – The new value to bind to.

Returns:

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

Return type:

ParameterExpression

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)

Returns a new Expression with replacement Parameters.

Parameters:

• parameter_map (dict) – Mapping from Parameters in self to the ParameterExpression instances with which they should be replaced.

• allow_unknown_parameters (bool) – If False, raises an error if parameter_map contains Parameters in the keys outside those present in the expression. If True, any such parameters are simply ignored.

Raises:

CircuitError –

• If parameter_map contains Parameters outside those in self. - If the replacement Parameters in parameter_map would result in a name conflict in the generated expression.

Returns:

A new expression with the specified parameters replaced.

Return type:

ParameterExpression

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