function - Cannot understand a C++ line -

i reading c++ code , came across function:

double nm_poissons_ratio(double /*temp*/)  {    double pr(0.0);    pr = 0.31;    return pr;  }

i don't understand effect of /* */ characters surround temp variable.

thanks

if write

double nm_poissons_ratio(double temp)

the compiler warning. unused variable.

in case, coder wanted retain signature reason, avoid warning. he/she therefore put comment show was.

why signature? it's hard know.

perhaps intermediate version of code, , he/she plans use parameter in future (this excellent case retain warning).
perhaps it's passed callback function expects specific signature.

Macro