Function

# cblas_drotg

Constructs a Givens rotation matrix.

## 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

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`.

### Double-Precision Float Matrix Functions

`cblas_dasum`

Computes the sum of the absolute values of elements in a vector (double-precision).

`cblas_daxpy`

Computes a constant times a vector plus a vector (double-precision).

`cblas_dcopy`

Copies a vector to another vector (double-precision).

`cblas_dgbmv`

Scales a general band matrix, then multiplies by a vector, then adds a vector (double precision).

`cblas_dgemm`

Multiplies two matrices (double-precision).

`cblas_dgemv`

Multiplies a matrix by a vector (double precision).

`cblas_dger`

Multiplies vector X by the transpose of vector Y, then adds matrix A (double precison).

`cblas_dnrm2`

Computes the L2 norm (Euclidian length) of a vector (double precision).

`cblas_drot`

Applies a Givens rotation matrix to a pair of vectors.

`cblas_drotm`

Applies a modified Givens transformation (single precision).

`cblas_drotmg`

Generates a modified Givens rotation matrix.

`cblas_dsbmv`

Scales a symmetric band matrix, then multiplies by a vector, then adds a vector (double precision).

`cblas_dscal`

Multiplies each element of a vector by a constant (double-precision).

`cblas_dspmv`

Scales a packed symmetric matrix, then multiplies by a vector, then scales and adds another vector (double precision).

`cblas_dspr`

Rank one update: adds a packed symmetric matrix to the product of a scaling factor, a vector, and its transpose (double precision).

`cblas_dspr2`

Rank two update of a packed symmetric matrix using two vectors (single precision).

`cblas_dswap`

Exchanges the elements of two vectors (double precision).

`cblas_dsymm`

Multiplies a matrix by a symmetric matrix (double-precision).

`cblas_dsymv`

Scales a symmetric matrix, multiplies by a vector, then scales and adds another vector (single precision).

`cblas_dsyr`

Rank one update: adds a symmetric matrix to the product of a scaling factor, a vector, and its transpose (double precision).

`cblas_dsyr2`

Rank two update of a symmetric matrix using two vectors (single precision).

`cblas_dsyr2k`

Performs a rank-2k update of a symmetric matrix (double precision).

`cblas_dsyrk`

Rank-k update—multiplies a symmetric matrix by its transpose and adds a second matrix (double precision).

`cblas_dtbmv`

Scales a triangular band matrix, then multiplies by a vector (double precision).

`cblas_dtbsv`

Solves a triangular banded system of equations.

`cblas_dtpmv`

Multiplies a triangular matrix by a vector, then adds a vector (double precision).

`cblas_dtpsv`

Solves a packed triangular system of equations.

`cblas_dtrmm`

Scales a triangular matrix and multiplies it by a matrix.

`cblas_dtrmv`

Multiplies a triangular matrix by a vector.

`cblas_dtrsm`

Solves a triangular system of equations with multiple values for the right side.

`cblas_dtrsv`

Solves a triangular system of equations with a single value for the right side.