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Technical Reference: Base Operating System and Extensions , Volume 2

SROT, DROT, CSROT, or ZDROT Subroutine

Purpose

Applies a plane rotation.

Library

BLAS Library (libblas.a)

FORTRAN Syntax

SUBROUTINE SROT(N,X,INCX,Y,INCY,C,S)
INTEGER INCX, INCY, N
REAL C, S
REAL X(*), Y(*)

```SUBROUTINE DROT(N,X,INCX,Y,INCY,C,S)
INTEGER INCX,INCY,N
DOUBLE PRECISION C,S
DOUBLE PRECISION X(*),Y(*)
```

```SUBROUTINE CSROT(N,X,INCX,Y,INCY,C,S)
INTEGER INCX,INCY,N
REAL C,S
COMPLEX X(*),Y(*)
```

```SUBROUTINE ZDROT(N,X,INCX,Y,INCY,C,S)
INTEGER INCX,INCY,N
DOUBLE PRECISION C,S
COMPLEX*16 X(*),Y(*)
```

Description

The SROT, DROT, CSROT, or ZDROT subroutine computes:

```---  ---      ---     ---     ---  ---
|  X   |      |  C   S  |     |  X   |
|   i  |      |         |     |   i  |
|      |  :=  |         |  .  |      |  for i = 1, ..., N.
|  Y   |      |         |     |  Y   |
|   i  |      | -S   C  |     |   i  |
---  ---      ---     ---     ---  ---
```

The subroutines return the modified X and Y.

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) ); unchanged on exit. INCX On entry, INCX specifies the increment for the elements of X; unchanged on exit. Y Vector of dimension at least (1 + (N-1) * abs(INCY) ); modified on exit. INCY On entry, INCY specifies the increment for the elements of Y; unchanged on exit. C Scalar constant; unchanged on exit. S Scalar constant; unchanged on exit.

Error Codes

If N <= 0, or if C = 1 and S = 0, the subroutines return immediately.

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