dasum daxpy dcopy ddot dnrm2 drot drotg drotm drotmg dscal dswap

drotg() void drotg ( double *  a, double *  b, double *  c, double *  s  ) Constructs Givens plane rotation (BLAS 1) Purpose This routine constructs Givens plane rotation for the point (a, b) as below. ( c s ) * ( a ) = ( r ) ( -s c ) ( b ) ( 0 ) where r = sign(sqrt(a^2 + b^2), a), if |a| > |b|, r = sign(sqrt(a^2 + b^2), b), if |a| <= |b|, c^2 + s^2 = 1. The constructed plane rotation can be used by drot to convert the points to the new coordinate system. Parameters [in,out] a [in] a value [out] r value [in,out] b [in] b value [out] z value   = s (if |a| > |b|)   = 1/c (|a| <= |b| and c != 0)   = 1 (if |a| <= |b| and c = 0)   = 0 (if r = 0) c and s can be reconstructed from z.   c = sqrt(1 - z^2), s = z (if z < 1)   c = 0, s = 1 (if z = 1)   c = 1/z, s = sqrt(1 - (1/z)^2) (if z > 1) [out] c c (cosine) value.   = a/r (if r != 0)   = 1 (if r = 0) [out] s s (sine) value.   = b/r (if r != 0)   = 0 (if r = 0) Reference BLAS