---
title: "sparse_extract_block_double(_:_:_:_:_:_:)"
framework: accelerate
role: symbol
role_heading: Function
path: "accelerate/sparse_extract_block_double(_:_:_:_:_:_:)"
---

# sparse_extract_block_double(_:_:_:_:_:_:)

Extracts values from a specified block of a double-precision matrix.

## Declaration

```swift
func sparse_extract_block_double(_ A: sparse_matrix_double!, _ bi: sparse_index, _ bj: sparse_index, _ row_stride: sparse_dimension, _ col_stride: sparse_dimension, _ val: UnsafeMutablePointer<Double>!) -> sparse_status
```

## Parameters

- `A`: The sparse matrix, A, which must have been created with doc://com.apple.accelerate/documentation/Accelerate/sparse_matrix_block_create_double(_:_:_:_:) or doc://com.apple.accelerate/documentation/Accelerate/sparse_matrix_variable_block_create_double(_:_:_:_:). doc://com.apple.accelerate/documentation/Accelerate/SPARSE_ILLEGAL_PARAMETER is returned if not met. A holds block dimensions (fixed or variable) set with matrix object creation routine.
- `bi`: The block row index for value extraction. Indices are 0 based (first block of matrix is A[0,0]). Indices expected to be in the bounds of matrix dimensions, undefined behavior if not met.
- `bj`: The block column index for value extraction. Indices are 0 based (first block of matrix is A[0,0]). Indices expected to be in the bounds of matrix dimensions, undefined behavior if not met.
- `row_stride`: The row stride in number of elements to move from one row to the next for the block val.
- `col_stride`: The column stride in number of elements to move from one column to the next for the block val.
- `val`: Pointer to dense block to place the extracted values. Expected to be of size K * L where K * L is the block size for the matrix object at block index bi,bj. This dimensions is set at matrix object creation time.

## Return Value

Return Value On success SPARSE_SUCCESS is return and val has been updated with the block from block index bi,bj. If A creation requirements are not met, SPARSE_ILLEGAL_PARAMETER is returned and val is unchanged.

## Discussion

Discussion Extract the bi,bj’th block from the sparse matrix A. 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.

## See Also

### Value extraction

- [sparse_extract_block_float(_:_:_:_:_:_:)](accelerate/sparse_extract_block_float(_:_:_:_:_:_:).md)
- [sparse_extract_block_double_complex(_:_:_:_:_:_:)](accelerate/sparse_extract_block_double_complex(_:_:_:_:_:_:).md)
- [sparse_extract_block_float_complex(_:_:_:_:_:_:)](accelerate/sparse_extract_block_float_complex(_:_:_:_:_:_:).md)