?lartgp

Syntax

FORTRAN 77:

call slartgp( f, g, cs, sn, r )

call dlartgp( f, g, cs, sn, r )

Fortran 95:

call lartgp( f,g,cs,sn,r )

Include Files

The FORTRAN 77 interfaces are specified in the mkl_lapack.fi include file (to be used in Fortran programs) and in the mkl_lapack.h include file (to be used in C programs).

Description

The routine generates a plane rotation so that

where cs² + sn² = 1

This is a slower, more accurate version of the BLAS Level 1 routine ?rotg, except for the following differences:

• f and g are unchanged on return.

• If g=0, then cs=(+/-)1 and sn=0.

• If f=0 and g ≠ 0, then cs=0 and sn=(+/-)1.

The sign is chosen so that r ≥ 0.

Input Parameters

f, g

REAL for slartgp

DOUBLE PRECISION for dlartgp

The first and second component of the vector to be rotated.

Output Parameters

cs

REAL for slartgp

DOUBLE PRECISION for dlartgp

The cosine of the rotation.

sn

REAL for slartgp

DOUBLE PRECISION for dlartgp

The sine of the rotation.

r

REAL for slartgp

DOUBLE PRECISION for dlartgp

The nonzero component of the rotated vector.

Fortran 95 Interface Notes

Routines in Fortran 95 interface have fewer arguments in the calling sequence than their FORTRAN 77 counterparts. For general conventions applied to skip redundant or reconstructible arguments, see Fortran 95 Interface Conventions.

Specific details for the routine ?lartgp interface are as follows:

f

Holds the first component of the vector to be rotated.

g

Holds the second component of the vector to be rotated.

cs

Holds the cosine of the rotation.

sn

Holds the sine of the rotation.

r

Holds the nonzero component of the rotated vector.