?rotm

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 4/28/2026

Version

Public

?rotm

Performs modified Givens rotation of points in the plane.

Syntax

void cblas_srotm(const MKL_INT n, float *x, const MKL_INT incx, float *y, const MKL_INT incy,
                 const float *param);

void cblas_drotm(const MKL_INT n, double *x, const MKL_INT incx, double *y, const MKL_INT incy,
                 const double *param);

Include Files

mkl.h

Description

Given two vectors \(x\) and \(y\) of length \(n\), each vector element of these vectors is replaced as follows:

\[\begin{split}\begin{bmatrix} x_i \\ y_i \end{bmatrix} = H \begin{bmatrix} x_i \\ y_i \end{bmatrix} \quad \textrm{for } i = 1, \dots, n \,,\end{split}\]

where \(H\) is a modified Givens transformation matrix whose values are specified by param. See discussion on the param input parameter.

Input Parameters

n

Specifies the number of elements in vectors x and y.

x

Array, size at least 1 + (n - 1) * abs(incx).

incx

Specifies the increment for the elements of x.

y

Array, size at least 1 + (n - 1) * abs(incy).

incy

Specifies the increment for the elements of y.

param

Array, size 5.

param[0] contains a switch. param[1] to param[4] may be used to set the elements of the matrix \(H\), \(h_{11}\), \(h_{21}\), \(h_{12}\), and \(h_{22}\), respectively. Depending on the value of param[0], the elements of \(H\) are set as follows:

param[0] = -1.0:

\[\begin{split}H = \begin{bmatrix} h_{11} & h_{12} \\ h_{21} & h_{22} \end{bmatrix}\end{split}\]

param[0] = 0.0:

\[\begin{split}H = \begin{bmatrix} 1.0 & h_{12} \\ h_{21} & 1.0 \end{bmatrix}\end{split}\]

param[0] = 1.0:

\[\begin{split}H = \begin{bmatrix} h_{11} & 1.0 \\ -1.0 & h_{22} \end{bmatrix}\end{split}\]

param[0] = -2.0:

\[\begin{split}H = \begin{bmatrix} 1.0 & 0.0 \\ 0.0 & 1.0 \end{bmatrix}\end{split}\]

In the last three cases, the matrix entries of 1.0, -1.0, and 0.0 are assumed based on the value of param[0] and are not required to be set in param.

Output Parameters

x: Each element x[i] is replaced by \(h_{11} \cdot {}\)x[i]\({} + h_{12} \cdot {}\)y[i].
y: Each element y[i] is replaced by \(h_{21} \cdot {}\)x[i]\({} + h_{22} \cdot {}\)y[i].

BLAS 95 Interface Notes

There exist FORTRAN 77 and FORTRAN 95 interfaces for this routine. See the Intel® oneMKL Fortran Developer Reference for details.

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Developer Reference for Intel® oneAPI Math Kernel Library for C

?rotm

Syntax

Include Files

Description

Input Parameters

Output Parameters

BLAS 95 Interface Notes