## Developer Reference

• 2020.2
• 07/15/2020
• Public Content
Contents

# ?rotmg

Computes the parameters for a modified Givens rotation.

## Syntax

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
:
h
11
,
h
21
,
h
12
, and
h
22
, 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.