# clartg.f90 - Man Page

SRC/clartg.f90

## Synopsis

### Functions/Subroutines

subroutine **clartg** (f, g, c, s, r)**CLARTG** generates a plane rotation with real cosine and complex sine.

## Function/Subroutine Documentation

### subroutine clartg (complex(wp) f, complex(wp) g, real(wp) c, complex(wp) s, complex(wp) r)

**CLARTG** generates a plane rotation with real cosine and complex sine.

**Purpose:**

CLARTG generates a plane rotation so that [ C S ] . [ F ] = [ R ] [ -conjg(S) C ] [ G ] [ 0 ] where C is real and C**2 + |S|**2 = 1. The mathematical formulas used for C and S are sgn(x) = { x / |x|, x != 0 { 1, x = 0 R = sgn(F) * sqrt(|F|**2 + |G|**2) C = |F| / sqrt(|F|**2 + |G|**2) S = sgn(F) * conjg(G) / sqrt(|F|**2 + |G|**2) Special conditions: If G=0, then C=1 and S=0. If F=0, then C=0 and S is chosen so that R is real. When F and G are real, the formulas simplify to C = F/R and S = G/R, and the returned values of C, S, and R should be identical to those returned by SLARTG. The algorithm used to compute these quantities incorporates scaling to avoid overflow or underflow in computing the square root of the sum of squares. This is the same routine CROTG fom BLAS1, except that F and G are unchanged on return. Below, wp=>sp stands for single precision from LA_CONSTANTS module.

**Parameters***F*F is COMPLEX(wp) The first component of vector to be rotated.

*G*G is COMPLEX(wp) The second component of vector to be rotated.

*C*C is REAL(wp) The cosine of the rotation.

*S*S is COMPLEX(wp) The sine of the rotation.

*R*R is COMPLEX(wp) The nonzero component of the rotated vector.

**Author**Weslley Pereira, University of Colorado Denver, USA

**Date**December 2021

**Further Details:**

Based on the algorithm from Anderson E. (2017) Algorithm 978: Safe Scaling in the Level 1 BLAS ACM Trans Math Softw 44:1--28 https://doi.org/10.1145/3061665

Definition at line **115** of file **clartg.f90**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page clartg(3) is an alias of clartg.f90(3).

Tue Nov 28 2023 12:08:41 Version 3.12.0 LAPACK