I'm unsure how to use functions that are declared as extern... I assume these are built-in functions in C that I can simply reference? But how do I do that?
Say, for example I want to use the built-in incomplete gamma function, that is
extern double igamc (double a, double x);
But I simply get a undefined reference compilation error: "Undefined reference to 'igamc'"
I've seen people use these functions, there are a whole list of them.
Thanks in advance