---
name: "rotmg"
section: "3"
platform: "linux"
package: "lapack-doc"
version: "3.12.1-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/rotmg"
---

# rotmg(3)

rotmg: generate modified (fast) plane rotation

## NAME

rotmg - rotmg: generate modified (fast) plane rotation

## SYNOPSIS

### Functions

subroutine **drotmg** (dd1, dd2, dx1, dy1, dparam)\
 **DROTMG**  subroutine **srotmg** (sd1, sd2, sx1, sy1, sparam)\
 **SROTMG**

## Detailed Description

## Function Documentation

### subroutine drotmg (double precision dd1, double precision dd2, double precision dx1, double precision dy1, double precision, dimension(5) dparam)

**DROTMG**

**Purpose:**

```
!>
!>    CONSTRUCT THE MODIFIED GIVENS TRANSFORMATION MATRIX H WHICH ZEROS
!>    THE SECOND COMPONENT OF THE 2-VECTOR  (DSQRT(DD1)*DX1,DSQRT(DD2)*>    DY2)**T.
!>    WITH DPARAM(1)=DFLAG, H HAS ONE OF THE FOLLOWING FORMS..
!>
!>    DFLAG=-1.D0     DFLAG=0.D0        DFLAG=1.D0     DFLAG=-2.D0
!>
!>      (DH11  DH12)    (1.D0  DH12)    (DH11  1.D0)    (1.D0  0.D0)
!>    H=(          )    (          )    (          )    (          )
!>      (DH21  DH22),   (DH21  1.D0),   (-1.D0 DH22),   (0.D0  1.D0).
!>    LOCATIONS 2-4 OF DPARAM CONTAIN DH11, DH21, DH12, AND DH22
!>    RESPECTIVELY. (VALUES OF 1.D0, -1.D0, OR 0.D0 IMPLIED BY THE
!>    VALUE OF DPARAM(1) ARE NOT STORED IN DPARAM.)
!>
!>    THE VALUES OF GAMSQ AND RGAMSQ SET IN THE DATA STATEMENT MAY BE
!>    INEXACT.  THIS IS OK AS THEY ARE ONLY USED FOR TESTING THE SIZE
!>    OF DD1 AND DD2.  ALL ACTUAL SCALING OF DATA IS DONE USING GAM.
!>
!>
```

**Parameters**

*DD1*

```
!>          DD1 is DOUBLE PRECISION
!>
```

*DD2*

```
!>          DD2 is DOUBLE PRECISION
!>
```

*DX1*

```
!>          DX1 is DOUBLE PRECISION
!>
```

*DY1*

```
!>          DY1 is DOUBLE PRECISION
!>
```

*DPARAM*

```
!>          DPARAM is DOUBLE PRECISION array, dimension (5)
!>     DPARAM(1)=DFLAG
!>     DPARAM(2)=DH11
!>     DPARAM(3)=DH21
!>     DPARAM(4)=DH12
!>     DPARAM(5)=DH22
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **89** of file **drotmg.f**.

### subroutine srotmg (real sd1, real sd2, real sx1, real sy1, real, dimension(5) sparam)

**SROTMG**

**Purpose:**

```
!>
!>    CONSTRUCT THE MODIFIED GIVENS TRANSFORMATION MATRIX H WHICH ZEROS
!>    THE SECOND COMPONENT OF THE 2-VECTOR  (SQRT(SD1)*SX1,SQRT(SD2)*>    SY2)**T.
!>    WITH SPARAM(1)=SFLAG, H HAS ONE OF THE FOLLOWING FORMS..
!>
!>    SFLAG=-1.E0     SFLAG=0.E0        SFLAG=1.E0     SFLAG=-2.E0
!>
!>      (SH11  SH12)    (1.E0  SH12)    (SH11  1.E0)    (1.E0  0.E0)
!>    H=(          )    (          )    (          )    (          )
!>      (SH21  SH22),   (SH21  1.E0),   (-1.E0 SH22),   (0.E0  1.E0).
!>    LOCATIONS 2-4 OF SPARAM CONTAIN SH11,SH21,SH12, AND SH22
!>    RESPECTIVELY. (VALUES OF 1.E0, -1.E0, OR 0.E0 IMPLIED BY THE
!>    VALUE OF SPARAM(1) ARE NOT STORED IN SPARAM.)
!>
!>    THE VALUES OF GAMSQ AND RGAMSQ SET IN THE DATA STATEMENT MAY BE
!>    INEXACT.  THIS IS OK AS THEY ARE ONLY USED FOR TESTING THE SIZE
!>    OF SD1 AND SD2.  ALL ACTUAL SCALING OF DATA IS DONE USING GAM.
!>
!>
```

**Parameters**

*SD1*

```
!>          SD1 is REAL
!>
```

*SD2*

```
!>          SD2 is REAL
!>
```

*SX1*

```
!>          SX1 is REAL
!>
```

*SY1*

```
!>          SY1 is REAL
!>
```

*SPARAM*

```
!>          SPARAM is REAL array, dimension (5)
!>     SPARAM(1)=SFLAG
!>     SPARAM(2)=SH11
!>     SPARAM(3)=SH21
!>     SPARAM(4)=SH12
!>     SPARAM(5)=SH22
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **89** of file **srotmg.f**.

## Author

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