---
title: "SparseUpdateFactor(_:_:_:_:_:)"
framework: accelerate
role: symbol
role_heading: Function
path: "accelerate/sparseupdatefactor(_:_:_:_:_:)-wrqg"
---

# SparseUpdateFactor(_:_:_:_:_:)

Apply a low-rank update to an existing factorization of a matrix of double values.

## Declaration

```swift
func SparseUpdateFactor(_ updateAlgorithm: SparseUpdate_t, _ Factorization: UnsafeMutablePointer<SparseOpaqueFactorization_Double>, _ updateCount: Int32, _ updatedIndices: UnsafePointer<Int32>, _ Update: SparseMatrix_Double)
```

## Parameters

- `updateAlgorithm`: The update algorithm to use
- `Factorization`: The existing factorization to be updated. The existing factorization will be modified and will no longer solve AX=B.
- `updateCount`: Number of updated entries or columns
- `updatedIndices`: List of updated indices, interpreted as described above
- `Update`: The updated entries.

## Discussion

Discussion If we have a factorization A = LU and now wish to solve a system ĀX = B where Ā = A + UV^T for some low-rank update matrices U of size m x k and V of size k x n for some small k there exist methods to modify (update) the original factors at a lower cost than a full factorization. Supported techniques are: SparseUpdatePartialRefactor: The most stable, but most expensive, method is to perform a partial refactorization that will recalculate the L and U factor values that would be different if performing an LU factorization from scratch. For the partial refactorization, updatedIndices should be a list of updateCount (row, column) pairs indicating modified values (i.e. a total of 2*updateCount integers), and Update should be a full copy of the original matrix with those value modified to their new values. The structure of Update must be identical to that of the original matrix.

## See Also

### Factorization update functions

- [SparseUpdateFactor(_:_:_:_:_:)](accelerate/sparseupdatefactor(_:_:_:_:_:)-1n2be.md)
- [SparseUpdateFactor(_:_:_:_:_:)](accelerate/sparseupdatefactor(_:_:_:_:_:)-9h956.md)
- [SparseUpdateFactor(_:_:_:_:_:)](accelerate/sparseupdatefactor(_:_:_:_:_:)-9qg54.md)