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

# cblas_drotg(_:_:_:_:)

Constructs a Givens rotation matrix.

## Declaration

```swift
func cblas_drotg(_ A: UnsafeMutablePointer<Double>, _ B: UnsafeMutablePointer<Double>, _ C: UnsafeMutablePointer<Double>, _ S: UnsafeMutablePointer<Double>)
```

## Parameters

- `A`: Double-precision value a. Overwritten on return with result r.
- `B`: Double-precision value b. Overwritten on return with result z (zero).
- `C`: Unused on entry. Overwritten on return with the value cos(θ).
- `S`: Unused on entry. Overwritten on return with the value sin(θ).

## Discussion

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.

## See Also

### Double-precision float matrix functions

- [cblas_dasum(_:_:_:)](accelerate/cblas_dasum(_:_:_:).md)
- [cblas_daxpy(_:_:_:_:_:_:)](accelerate/cblas_daxpy(_:_:_:_:_:_:).md)
- [cblas_dcopy(_:_:_:_:_:)](accelerate/cblas_dcopy(_:_:_:_:_:).md)
- [cblas_dgbmv(_:_:_:_:_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dgbmv(_:_:_:_:_:_:_:_:_:_:_:_:_:_:).md)
- [cblas_dgemm(_:_:_:_:_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dgemm(_:_:_:_:_:_:_:_:_:_:_:_:_:_:).md)
- [cblas_dgemv(_:_:_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dgemv(_:_:_:_:_:_:_:_:_:_:_:_:).md)
- [cblas_dger(_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dger(_:_:_:_:_:_:_:_:_:_:).md)
- [cblas_dnrm2(_:_:_:)](accelerate/cblas_dnrm2(_:_:_:).md)
- [cblas_drot(_:_:_:_:_:_:_:)](accelerate/cblas_drot(_:_:_:_:_:_:_:).md)
- [cblas_drotm(_:_:_:_:_:_:)](accelerate/cblas_drotm(_:_:_:_:_:_:).md)
- [cblas_drotmg(_:_:_:_:_:)](accelerate/cblas_drotmg(_:_:_:_:_:).md)
- [cblas_dsbmv(_:_:_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dsbmv(_:_:_:_:_:_:_:_:_:_:_:_:).md)
- [cblas_dscal(_:_:_:_:)](accelerate/cblas_dscal(_:_:_:_:).md)
- [cblas_dspmv(_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dspmv(_:_:_:_:_:_:_:_:_:_:).md)
- [cblas_dspr(_:_:_:_:_:_:_:)](accelerate/cblas_dspr(_:_:_:_:_:_:_:).md)