?rotmg

Syntax

call srotmg(d1, d2, x1, y1, param)

call drotmg(d1, d2, x1, y1, param)

call rotmg(d1, d2, x1, y1, param)

Include Files

• mkl.fi, blas.f90

Description

Given Cartesian coordinates (x1, y1) of an input vector, these routines compute the components of a modified Givens transformation matrix H that zeros the y-component of the resulting vector:

Input Parameters

d1

REAL for srotmg

DOUBLE PRECISION for drotmg

Provides the scaling factor for the x-coordinate of the input vector.

d2

REAL for srotmg

DOUBLE PRECISION for drotmg

Provides the scaling factor for the y-coordinate of the input vector.

x1

REAL for srotmg

DOUBLE PRECISION for drotmg

Provides the x-coordinate of the input vector.

y1

REAL for srotmg

DOUBLE PRECISION for drotmg

Provides the y-coordinate of the input vector.

Output Parameters

d1

REAL for srotmg

DOUBLE PRECISION for drotmg

Provides the first diagonal element of the updated matrix.

d2

REAL for srotmg

DOUBLE PRECISION for drotmg

Provides the second diagonal element of the updated matrix.

x1

REAL for srotmg

DOUBLE PRECISION for drotmg

Provides the x-coordinate of the rotated vector before scaling.

param

REAL for srotmg

DOUBLE PRECISION for drotmg

Array, size 5.

The elements of the param array are:

param(1) contains a switch, flag. the other array elements param(2-5) contain the components of the array H: h₁₁, h₂₁, h₁₂, and h₂₂, respectively.

Depending on the values of flag, the components of H are set as follows:

flag = -1.0:

flag = 0.0:

flag = 1.0:

flag = -2.0:

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