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

# CollectAndCollapse

*class* `qiskit.transpiler.passes.CollectAndCollapse(*args, **kwargs)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/transpiler/passes/optimization/collect_and_collapse.py#L23-L88)

Bases: [`TransformationPass`](/docs/api/qiskit/qiskit.transpiler.TransformationPass "qiskit.transpiler.basepasses.TransformationPass")

A general transpiler pass to collect and to consolidate blocks of nodes in a circuit.

This transpiler pass depends on two functions: the collection function and the collapsing function. The collection function `collect_function` takes a DAG and returns a list of blocks. The collapsing function `collapse_function` takes a DAG and a list of blocks, consolidates each block, and returns the modified DAG.

The input and the output DAGs are of type [`DAGCircuit`](/docs/api/qiskit/qiskit.dagcircuit.DAGCircuit "qiskit.dagcircuit.DAGCircuit"), however when exploiting commutativity analysis to collect blocks, the [`DAGDependency`](/docs/api/qiskit/qiskit.dagcircuit.DAGDependency "qiskit.dagcircuit.DAGDependency") representation is used internally. To support this, the `collect_function` and `collapse_function` should work with both types of DAGs and DAG nodes.

Other collection and consolidation transpiler passes, for instance [`CollectLinearFunctions`](/docs/api/qiskit/qiskit.transpiler.passes.CollectLinearFunctions "qiskit.transpiler.passes.CollectLinearFunctions"), may derive from this pass, fixing `collect_function` and `collapse_function` to specific functions.

**Parameters**

- **collect\_function** (*callable*) – a function that takes a DAG and returns a list of “collected” blocks of nodes
- **collapse\_function** (*callable*) – a function that takes a DAG and a list of “collected” blocks, and consolidates each block.
- **do\_commutative\_analysis** ([*bool*](https://docs.python.org/3/library/functions.html#bool)) – if True, exploits commutativity relations between nodes.

## Attributes

### is\_analysis\_pass

Check if the pass is an analysis pass.

If the pass is an AnalysisPass, that means that the pass can analyze the DAG and write the results of that analysis in the property set. Modifications on the DAG are not allowed by this kind of pass.

### is\_transformation\_pass

Check if the pass is a transformation pass.

If the pass is a TransformationPass, that means that the pass can manipulate the DAG, but cannot modify the property set (but it can be read).

## Methods

### execute

`execute(passmanager_ir, state, callback=None)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/transpiler/basepasses.py#L162-L181)

Execute optimization task for input Qiskit IR.

**Parameters**

- **passmanager\_ir** ([*DAGCircuit*](/docs/api/qiskit/qiskit.dagcircuit.DAGCircuit "qiskit._accelerate.circuit.DAGCircuit")) – Qiskit IR to optimize.
- **state** ([*DAGCircuit*](/docs/api/qiskit/qiskit.dagcircuit.DAGCircuit "qiskit._accelerate.circuit.DAGCircuit")) – State associated with workflow execution by the pass manager itself.
- **callback** ([*Callable*](https://docs.python.org/3/library/collections.abc.html#collections.abc.Callable)*\[\[*[*Task*](/docs/api/qiskit/qiskit.passmanager.Task "qiskit.passmanager.base_tasks.Task")*,* [*DAGCircuit*](/docs/api/qiskit/qiskit.dagcircuit.DAGCircuit "qiskit._accelerate.circuit.DAGCircuit")*,* [*PropertySet*](/docs/api/qiskit/qiskit.passmanager.PropertySet "qiskit.passmanager.compilation_status.PropertySet")*,* [*float*](https://docs.python.org/3/library/functions.html#float)*,* [*int*](https://docs.python.org/3/library/functions.html#int)*], None] | None*) – A callback function which is called per execution of optimization task.

**Returns**

Optimized Qiskit IR and state of the workflow.

**Return type**

[tuple](https://docs.python.org/3/library/stdtypes.html#tuple)\[[*DAGCircuit*](/docs/api/qiskit/qiskit.dagcircuit.DAGCircuit "qiskit._accelerate.circuit.DAGCircuit"), [*PassManagerState*](/docs/api/qiskit/qiskit.passmanager.PassManagerState "qiskit.passmanager.compilation_status.PassManagerState")]

### name

`name()`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/passmanager/base_tasks.py#L72-L74)

Name of the pass.

**Return type**

[str](https://docs.python.org/3/library/stdtypes.html#str)

### run

`run(dag)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/transpiler/passes/optimization/collect_and_collapse.py#L65-L88)

Run the CollectLinearFunctions pass on dag. :param dag: the DAG to be optimized. :type dag: DAGCircuit

**Returns**

the optimized DAG.

**Return type**

[DAGCircuit](/docs/api/qiskit/qiskit.dagcircuit.DAGCircuit "qiskit.dagcircuit.DAGCircuit")

### update\_status

`update_status(state, run_state)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.5/qiskit/transpiler/basepasses.py#L183-L191)

Update workflow status.

**Parameters**

- **state** ([*PassManagerState*](/docs/api/qiskit/qiskit.passmanager.PassManagerState "qiskit.passmanager.compilation_status.PassManagerState")) – Pass manager state to update.
- **run\_state** (*RunState*) – Completion status of current task.

**Returns**

Updated pass manager state.

**Return type**

[*PassManagerState*](/docs/api/qiskit/qiskit.passmanager.PassManagerState "qiskit.passmanager.compilation_status.PassManagerState")