I have to solve the Xin-She Yang N. 4 Function using Evolution Strategies.
This is the function:
$f(\bar x)=f(x_1, ..., x_n)=\left(\sum_{i=1}^{n}\sin^2(x_i)-e^{-\sum_{i=1}^{n}x_i^2}\right)e^{-\sum_{i=1}^{n}{\sin^2\sqrt{|x_i|}}}$
There are two $\sin$ in the function.
How can I know if the values $x_1, ..., x_n$ are in degrees or radians?
In any math beyond basic trig the arguments of trig functions are in radians. The only advantage of degrees is that simple angles come out with simple whole numbers of degrees. This does not compensate for the unnatural derivatives, integrals, Taylor series, etc. that come from degrees. You could certainly define $y_i=\frac {180}{\pi}x_i$ and write your sine functions in degrees if you want.