?rotg

Syntax

call srotg(a, b, c, s)

call drotg(a, b, c, s)

call crotg(a, b, c, s)

call zrotg(a, b, c, s)

call rotg(a, b, c, s)

Include Files

• mkl.fi, blas.f90

Description

Given the Cartesian coordinates (a, b) of a point, these routines return the parameters c, s, r, and z associated with the Givens rotation. The parameters c and s define a unitary matrix such that:

The parameter z is defined such that if |a| > |b|, z is s; otherwise if c is not 0 z is 1/c; otherwise z is 1.

See a more accurate LAPACK version ?lartg.

Input Parameters

a

REAL for srotg

DOUBLE PRECISION for drotg

COMPLEX for crotg

DOUBLE COMPLEX for zrotg

Provides the x-coordinate of the point p.

b

REAL for srotg

DOUBLE PRECISION for drotg

COMPLEX for crotg

DOUBLE COMPLEX for zrotg

Provides the y-coordinate of the point p.

Output Parameters

a

Contains the parameter r associated with the Givens rotation.

b

Contains the parameter z associated with the Givens rotation.

c

REAL for srotg

DOUBLE PRECISION for drotg

REAL for crotg

DOUBLE PRECISION for zrotg

Contains the parameter c associated with the Givens rotation.

s

REAL for srotg

DOUBLE PRECISION for drotg

COMPLEX for crotg

DOUBLE COMPLEX for zrotg

Contains the parameter s associated with the Givens rotation.