--- title: ParameterExpression (v0.46) description: API reference for qiskit.circuit.ParameterExpression in qiskit v0.46 source: https://eu-de.quantum.cloud.ibm.com/docs/en/api/qiskit/0.46/qiskit.circuit.ParameterExpression --- # ParameterExpression *class* `qiskit.circuit.ParameterExpression(symbol_map, expr)` [GitHub](https://github.com/qiskit/qiskit/tree/stable/0.46/qiskit/circuit/parameterexpression.py) Bases: [`object`](https://docs.python.org/3/library/functions.html#object) ParameterExpression class to enable creating expressions of Parameters. Create a new [`ParameterExpression`](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression"). Not intended to be called directly, but to be instantiated via operations on other [`Parameter`](/docs/api/qiskit/0.46/qiskit.circuit.Parameter "qiskit.circuit.Parameter") or [`ParameterExpression`](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression") objects. **Parameters** - **symbol\_map** (*Dict\[*[*Parameter*](/docs/api/qiskit/0.46/qiskit.circuit.Parameter "qiskit.circuit.Parameter")*, \[*[*ParameterExpression*](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression")*,* [*float*](https://docs.python.org/3/library/functions.html#float)*, or* [*int*](https://docs.python.org/3/library/functions.html#int)*]]*) – Mapping of [`Parameter`](/docs/api/qiskit/0.46/qiskit.circuit.Parameter "qiskit.circuit.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 `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*](/docs/api/qiskit/0.46/qiskit.circuit.Parameter "qiskit.circuit.Parameter")) – A parameter in this expression whose value will be updated. - **value** ([*ParameterExpression*](#qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression") *|*[*float*](https://docs.python.org/3/library/functions.html#float)) – The new value to bind to. **Returns** A new expression parameterized by any parameters which were not bound by assignment. **Return type** [*ParameterExpression*](#qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression") ### bind `bind(parameter_values, allow_unknown_parameters=False)` Binds the provided set of parameters to their corresponding values. **Parameters** - **parameter\_values** ([*dict*](https://docs.python.org/3/library/stdtypes.html#dict)) – Mapping of Parameter instances to the numeric value to which they will be bound. - **allow\_unknown\_parameters** ([*bool*](https://docs.python.org/3/library/functions.html#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**](/docs/api/qiskit/0.46/circuit#qiskit.circuit.CircuitError "qiskit.circuit.CircuitError") – - If parameter\_values contains Parameters outside those in self. - If a non-numeric value is passed in parameter\_values. - [**ZeroDivisionError**](https://docs.python.org/3/library/exceptions.html#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*](#qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression") ### conjugate `conjugate()` Return the conjugate. **Return type** [*ParameterExpression*](#qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.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*](/docs/api/qiskit/0.46/qiskit.circuit.Parameter "qiskit.circuit.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*](#qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression") | [complex](https://docs.python.org/3/library/functions.html#complex) ### 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)` Returns a new Expression with replacement Parameters. **Parameters** - **parameter\_map** ([*dict*](https://docs.python.org/3/library/stdtypes.html#dict)) – Mapping from Parameters in self to the ParameterExpression instances with which they should be replaced. - **allow\_unknown\_parameters** ([*bool*](https://docs.python.org/3/library/functions.html#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**](/docs/api/qiskit/0.46/circuit#qiskit.circuit.CircuitError "qiskit.circuit.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*](#qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression") ### 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