qiskit-documentation/docs/api/qiskit/0.32/qiskit.circuit.ParameterExpression.mdx

---
title: ParameterExpression
description: API reference for qiskit.circuit.ParameterExpression
in_page_toc_min_heading_level: 1
python_api_type: class
python_api_name: qiskit.circuit.ParameterExpression
---

# ParameterExpression

<Class id="qiskit.circuit.ParameterExpression" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.18/qiskit/circuit/parameterexpression.py" signature="ParameterExpression(symbol_map, expr)" modifiers="class">
  Bases: `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`](qiskit.circuit.Parameter "qiskit.circuit.Parameter") or [`ParameterExpression`](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression") objects.

  **Parameters**

  *   **symbol\_map** (*Dict\[*[*Parameter*](qiskit.circuit.Parameter "qiskit.circuit.Parameter")*, \[*[*ParameterExpression*](#qiskit.circuit.ParameterExpression "qiskit.circuit.ParameterExpression")*, float, or int]]*) – Mapping of [`Parameter`](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.

  ## Methods

  ### arccos

  <Function id="qiskit.circuit.ParameterExpression.arccos" signature="ParameterExpression.arccos()">
    Arccos of a ParameterExpression
  </Function>

  ### arcsin

  <Function id="qiskit.circuit.ParameterExpression.arcsin" signature="ParameterExpression.arcsin()">
    Arcsin of a ParameterExpression
  </Function>

  ### arctan

  <Function id="qiskit.circuit.ParameterExpression.arctan" signature="ParameterExpression.arctan()">
    Arctan of a ParameterExpression
  </Function>

  ### assign

  <Function id="qiskit.circuit.ParameterExpression.assign" signature="ParameterExpression.assign(parameter, value)">
    Assign one parameter to a value, which can either be numeric or another parameter expression.

    **Parameters**

    *   **parameter** ([*Parameter*](qiskit.circuit.Parameter "qiskit.circuit.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.
  </Function>

  ### bind

  <Function id="qiskit.circuit.ParameterExpression.bind" signature="ParameterExpression.bind(parameter_values)">
    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.

    **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.
  </Function>

  ### conjugate

  <Function id="qiskit.circuit.ParameterExpression.conjugate" signature="ParameterExpression.conjugate()">
    Return the conjugate.

    **Return type**

    `ParameterExpression`
  </Function>

  ### cos

  <Function id="qiskit.circuit.ParameterExpression.cos" signature="ParameterExpression.cos()">
    Cosine of a ParameterExpression
  </Function>

  ### exp

  <Function id="qiskit.circuit.ParameterExpression.exp" signature="ParameterExpression.exp()">
    Exponential of a ParameterExpression
  </Function>

  ### gradient

  <Function id="qiskit.circuit.ParameterExpression.gradient" signature="ParameterExpression.gradient(param)">
    Get the derivative of a parameter expression w\.r.t. a specified parameter expression.

    **Parameters**

    **param** ([*Parameter*](qiskit.circuit.Parameter "qiskit.circuit.Parameter")) – Parameter w\.r.t. which we want to take the derivative

    **Return type**

    `Union`\[`ParameterExpression`, `float`]

    **Returns**

    ParameterExpression representing the gradient of param\_expr w\.r.t. param
  </Function>

  ### is\_real

  <Function id="qiskit.circuit.ParameterExpression.is_real" signature="ParameterExpression.is_real()">
    Return whether the expression is real
  </Function>

  ### log

  <Function id="qiskit.circuit.ParameterExpression.log" signature="ParameterExpression.log()">
    Logarithm of a ParameterExpression
  </Function>

  ### sin

  <Function id="qiskit.circuit.ParameterExpression.sin" signature="ParameterExpression.sin()">
    Sine of a ParameterExpression
  </Function>

  ### subs

  <Function id="qiskit.circuit.ParameterExpression.subs" signature="ParameterExpression.subs(parameter_map)">
    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.

    **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.

    **Return type**

    `ParameterExpression`

    **Returns**

    A new expression with the specified parameters replaced.
  </Function>

  ### tan

  <Function id="qiskit.circuit.ParameterExpression.tan" signature="ParameterExpression.tan()">
    Tangent of a ParameterExpression
  </Function>

  ## Attributes

  ### parameters

  <Attribute id="qiskit.circuit.ParameterExpression.parameters">
    Returns a set of the unbound Parameters in the expression.

    **Return type**

    `Set`
  </Attribute>
</Class>