# SparseCreateSubfactor(_:_:) Returns an opaque object representing a sub-factor of a factorization in complex double. ``` func SparseCreateSubfactor(_ subfactor: SparseSubfactor_t, _ Factor: SparseOpaqueFactorization_Complex_Double) -> SparseOpaqueSubfactor_Complex_Double ``` ## Parameters `subfactor` The sub-factor the new object should represent. `Factor` The factorization to extract the sub-factor from. ## Return Value Object representing the requested sub-factor. Must be cleaned up by a call to `SparseCleanup` once it is no longer required. ## Discussion Here the term “sub-factor” is used to mean one or more parts of the whole factorization. For example, just the `Q` factor from `A=QRP`. The returned object is a wrapper around the orignal factorization, and does not actually perform any extraction (sub-factors are stored in non-standard formats that exploit implicit structure for efficiency, and formation of the sub-factor explicitly can be expensive). It is intended to be used as an argument to `SparseMultiply` and `SparseSolve` functions only. As `Factor` is contained in the returned object, its underlying reference count in incremented, and the returned object must hence be destroyed through a call to `SparseCleanup` to prevent a memory leak (however it is safe to call `SparseCleanup` on the original factorization whilst this object is still being used). --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)