# order The user-supplied array for ordering. ``` var order: UnsafeMutablePointer? ``` ## Discussion This property may be either `null` or a pointer to a permutation that reduces fill in the matrix that you’re factoring. The factor function encodes each element, `i`, as the `order[i]`-th position. For example, to order columns as `0, 4, 2, 1, 3`, specify this property as `[0, 3, 2, 4, 1]`. That is, the ordering that you specify is the inverse of the column ordering. The following code shows that `order[invp[i]]` equals `i` for all values of `i`: ```swift let order = [0, 3, 2, 4, 1] let invp = [0, 4, 2, 1, 3] // Prints "[0, 1, 2, 3, 4]". print((0 ..< 5).map { order[invp[$0]] }) ``` If [`orderMethod`](/documentation/Accelerate/SparseSymbolicFactorOptions/orderMethod) is [`SparseOrderUser`](/documentation/Accelerate/SparseOrderUser), and this pointer is `null`, the factor function uses the original matrix ordering. If [`orderMethod`](/documentation/Accelerate/SparseSymbolicFactorOptions/orderMethod) is [`SparseOrderUser`](/documentation/Accelerate/SparseOrderUser), and this pointer is nonnull, the factor function uses the user-provided permutation to order the matrix before factorization. The system may heuristically reinterpret the order to increase performance. Such reorderings don’t significantly increase fill in the factors *L*. If [`orderMethod`](/documentation/Accelerate/SparseSymbolicFactorOptions/orderMethod) isn’t [`SparseOrderUser`](/documentation/Accelerate/SparseOrderUser), the factor function computes its own fill-reducing ordering. If this pointer is nonnull, the factor function returns the computed permutation in the array. Pivoted factorizations may alter the actual permutation during the numerical factorization step. --- 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)