# sparse_unpack_vector_double(_:_:_:_:_:_:_:) Extracts elements from the sparse vector *x* into the corresponding location in the dense vector *y*, with both vectors containing double-precision values. ``` func sparse_unpack_vector_double(_ N: sparse_dimension, _ nz: sparse_dimension, _ zero: Bool, _ x: UnsafePointer!, _ indx: UnsafePointer!, _ y: UnsafeMutablePointer!, _ incy: sparse_stride) ``` ## Parameters `N` The number of elements in the dense vector *y*. `nz` The number of nonzero entries in the sparse vector *x*. `zero` When , zero the elements of *y* which do not have nonzero values written to them. When ignore the elements of *y* which do not have nonzero values written to them. `x` Pointer to the dense storage for the values of the sparse vector *x*. The corresponding entry in `indx` holds the index of the value. Contains `nz` values. `indx` Pointer to the dense storage for the index values of the sparse vector *x*. The corresponding entry in *x* holds the values of the vector. Contains `nz` values. Indices are always assumed to be stored in ascending order. Additionally, indices are assumed to be unique. Undefined behavior if either of these assumptions are not met.All indices are 0 based (the first element of a pointer is `ptr[0]` ). `y` Pointer to the dense vector y. Expected to be of size `N * abs(incy)` elements. Negative strides are supported. Note, unlike dense BLAS routines, the pointer points to the last element when stride is negative. On exit, the entries described by the indices in `indx` will be filled with the corresponding values in `x` and all other values will be unchanged if parameter zero is , or set to zero if parameter zero is . `incy` Increment between valid values in the dense vector y. Negative strides are supported. ## Discussion This function extracts elements from the sparse vector *x* into the corresponding location in the dense vector *y*. It can optionally zero the unused values of *y* by setting the `zero` parameter to . The function is equivalent to the following code. ```objc if (zero) for (i in 0 .. N-1) y[i*incy] = 0; for (i in 0 .. nz-1) if (indx[i] < N) y[indx[i]*incy] = x[i]; ``` On exit, *y* has been updated with the nonzero values. If `nz` is less than or equal to zero, *y* is unchanged. > Important: > Apple provides the BLAS and LAPACK libraries under the Accelerate framework to be in line with LAPACK 3.9.1. Starting with iOS 26, iPadOS 26, macOS 26, tvOS 26, visionOS 26, and watchOS 26, the libraries are in line with LAPACK 3.12.0. These new interfaces provide additional functionality, as well as a new ILP64 interface. To use the new interfaces, define `ACCELERATE_NEW_LAPACK` before including the Accelerate or vecLib headers. For ILP64 interfaces, also define `ACCELERATE_LAPACK_ILP64`. For Swift projects, specify `ACCELERATE_NEW_LAPACK=1` and `ACCELERATE_LAPACK_ILP64=1` as preprocessor macros in Xcode build settings under Apple Clang - Preprocessing > Preprocessor Macros. --- 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)