# cblas_drotmg(_:_:_:_:_:) Generates a modified Givens rotation matrix. ``` func cblas_drotmg(_ D1: UnsafeMutablePointer, _ D2: UnsafeMutablePointer, _ B1: UnsafeMutablePointer, _ B2: Double, _ P: UnsafeMutablePointer) ``` ## Parameters `D1` Scaling factor `D1`. `D2` Scaling factor `D2`. `B1` Scaling factor `B1`. `B2` Scaling factor `B2`. `P` A 5-element vector: - `P[0]`: Flag value that defines the form of matrix `H`. `-2.0` : matrix `H` contains the identity matrix. `-1.0` : matrix `H` is identical to matrix `SH` (defined by the remaining values in the vector). `0.0` : `H[1,2]` and `H[2,1]` are obtained from matrix `SH` . The remaining values are both `1.0` . `1.0` : `H[1,1]` and `H[2,2]` are obtained from matrix `SH` . `H[1,2]` is 1.0. `H[2,1]` is -1.0. - `P[1]`: Contains `SH[1,1]`. - `P[2]`: Contains `SH[2,1]`. - `P[3]`: Contains `SH[1,2]`. - `P[4]`: Contains `SH[2,2]`. ## Discussion The resulting matrix zeroes the second component of the vector `(sqrt(D1)*B1, sqrt(SD2)*B2)`. > 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)