20if (!function_exists(__NAMESPACE__ . 
'\\rho')) {
 
   21    function rho($complex): float
 
   23        $complex = Complex::validateComplexArgument($complex);
 
   26            ($complex->getReal() * $complex->getReal()) +
 
   27            ($complex->getImaginary() * $complex->getImaginary())
 
An exception for terminatinating execution or to throw for unit testing.