order
The user-supplied array for ordering.
Declaration
var order: UnsafeMutablePointer<Int32>?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:
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 is SparseOrderUser, and this pointer is null, the factor function uses the original matrix ordering.
If orderMethod is 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 isn’t 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.