---
title: simplify (latest version)
description: API reference for qiskit_fermions.transpiler.passes.synthesis.simplify in the latest version of qiskit-fermions
source: https://quantum.cloud.ibm.com/docs/en/api/qiskit-fermions/transpiler-passes-synthesis-simplify
---

# simplify

`simplify(mapper_fn)`

Wraps a mapper function so that it simplifies the operator it returns.

Simplifying merges duplicate Pauli terms and, as a side effect, sorts the terms into a canonical order. That order is worth asking for explicitly in two situations:

1. The term order an unsimplified mapper produces is **not** guaranteed to be stable between runs, because the operators of the Rust core do not preserve the order their terms were added in. A product formula synthesizes the terms in the order it receives them, so an unsimplified mapper can yield a different (though equally valid) circuit each time. Simplifying pins it.
2. It merges terms that map to the same Pauli string, which shortens the synthesized circuit when a mapper produces such duplicates.

Use it to wrap any `MapperFunction`:

```python
MapperFnEvolutionSynthesis(simplify(jordan_wigner))
```

**Parameters**

**mapper\_fn** ([*Callable*](https://docs.python.org/3/library/collections.abc.html#collections.abc.Callable)*\[\[*[*OperatorTrait*](/docs/api/qiskit-fermions/operators-operator-trait "qiskit_fermions.operators.operator_trait.OperatorTrait")*,* [*int*](https://docs.python.org/3/builtins/functions.html#int)*],* [*SparseObservable*](/docs/api/qiskit/qiskit.quantum_info.SparseObservable)*]*) – the mapper function to wrap.

**Returns**

A mapper function that simplifies whatever `mapper_fn` returns.

**Return type**

[*Callable*](https://docs.python.org/3/library/collections.abc.html#collections.abc.Callable)\[\[[*OperatorTrait*](/docs/api/qiskit-fermions/operators-operator-trait "qiskit_fermions.operators.operator_trait.OperatorTrait"), [int](https://docs.python.org/3/builtins/functions.html#int)], [*SparseObservable*](/docs/api/qiskit/qiskit.quantum_info.SparseObservable)]