naginterfaces.library.blas.zcsg

naginterfaces.library.blas.zcsg(t)

zcsg reconstructs the parameters $c$ (real) and $s$ (complex) of a complex plane rotation from the tangent of that rotation.

For full information please refer to the NAG Library document for f06cc

https://support.nag.com/numeric/nl/nagdoc_30/flhtml/f06/f06ccf.html

Parameters

tcomplex

The value $t$, the tangent of the rotation.

Returns

cfloat

The value $c$, the cosine of the rotation.

scomplex

The value $s$, the sine of the rotation.

Notes

No equivalent traditional C interface for this routine exists in the NAG Library.

zcsg reconstructs the parameters $c$ (real) and $s$ (complex) of a complex plane rotation, from the value of the tangent $t$, as returned by zrotgc():

$$c=\frac{1}{\sqrt{1+{\left|t\right|}^2}}\text{,}s=ct\text{,}$$

so that $c$ is always real and non-negative.

If $\left|t\right|<\sqrt{ϵ}$, where $ϵ$ is the machine precision, the function sets $c=1$ and $s=t$.