# cblas_zrotg(_:_:_:_:) Constructs a complex Givens rotation. ``` func cblas_zrotg(_ A: OpaquePointer, _ B: OpaquePointer, _ C: UnsafeMutablePointer, _ S: OpaquePointer) ``` ## Parameters `A` Complex value `a`. Overwritten on return with result `r`. `B` Complex value `a`. Overwritten on return with result `z` (zero). `C` Real value `c`. Unused on entry. Overwritten on return with the value `cos(θ)`. `S` Complex value `s`. Unused on entry. Overwritten on return with the value `sin(θ)`. ## Discussion Given a vertical matrix containing `a` and `b`, computes the values of `cos θ` and `sin θ` that zero the lower value (`b`). Returns the value of `sin θ` in `s`, the value of `cos θ` in `c`, and the upper value (`r`) in `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. --- 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)