[ Previous |
Next |
Contents |
Glossary |
Home |
Search ]

*AIX Version 4.3 Base Operating System and Extensions Technical Reference, Volume 2*

## SROTM or DROTM Subroutine

### Purpose

Applies the modified Givens transformation.

### Library

BLAS Library (**libblas.a**)

### FORTRAN Syntax

**SUBROUTINE SROTM(***N***,***X***,***INCX***,***Y***,***INCY***,***PARAM***)**
**INTEGER ***N***,***INCX***,***INCY*
**REAL ***X***(*),***Y***(****)***,***PARAM***(5)**

**SUBROUTINE DROTM(***N***,***X***,***INCX***,***Y***,***INCY***,***PARAM***)**
**INTEGER ***N***,***INCX***,***INCY*
**DOUBLE PRECISION ***X***(*),***Y***(*),***PARAM***(5)**

### Description

Let H denote the modified Givens transformation defined by the parameter array *PARAM*. The **SROTM** or **DROTM** subroutine computes:

--- --- --- ---
| x | | x |
| | := H * | |
| y | | y |
--- --- --- ---

where H is a 2 x 2 matrix with the components defined by the elements of the array *PARAM* as follows:

if *PARAM*(1) == 0.0
H(1,1) = H(2,2) = 1.0
H(2,1) = *PARAM*(3)
H(1,2) = *PARAM*(4)

if *PARAM*(1) == 1.0
H(1,2) = H(2,1) = -1.0
H(1,1) = *PARAM*(2)
H(2,2) = *PARAM*(5)

if *PARAM*(1) == -1.0
H(1,1) = *PARAM*(2)
H(2,1) = *PARAM*(3)
H(1,2) = *PARAM*(4)
H(2,2) = *PARAM*(5)

if *PARAM*(1) == -2.0
H = I (Identity matrix)

### Parameters

*N* |
On entry, *N* specifies the number of elements in *X* and *Y*; unchanged on exit. |

*X* |
Vector of dimension at least (1 + (*N*-1) * abs(*INCX*) ); on exit, modified as described above. |

*INCX* |
On entry, *INCX* specifies the increment for the elements of *X*; *INCX* must be greater than 0; unchanged on exit. |

*Y* |
Vector of dimension at least (1 + (*N*-1) * abs(*INCY*) ); on exit, modified as described above. |

*INCY* |
On entry, *INCY* specifies the increment for the elements of *Y*; *INCY* must be greater than 0; unchanged on exit. |

*PARAM* |
Vector of dimension (5); on entry, must be set as described above. Specifically, *PARAM*(1) is a flag and must have value of either 0.0, -1.0, 1.0, or 2.0; unchanged on exit. |

### Implementation Specifics

If *N* <= 0 or H is an identity matrix, the subroutines return immediately.

### Related information

The **SROTMG** or **DROTMG** subroutine builds the *PARAM* array prior to use by the **SROTM** or **DROTM** subroutine.

[ Previous |
Next |
Contents |
Glossary |
Home |
Search ]