Compiler warning from `ibeta_inverse.hpp` if asserts are disabled.

[WardBrian]

Compiling with -Wall -DBOOST_DISABLE_ASSERTS causes an unused variable warning from code added in #1004

Example:

// file boost.cpp
#include <boost/math/special_functions/beta.hpp>
#include <iostream>

int main(int argc, char** argv) {

    double a = argc;
    std::cout << boost::math::ibeta_inv(a,0.4,0.2);

    return 0;
}

$ g++ -Wall -DBOOST_DISABLE_ASSERTS -I./boost_1.84.0/ boost.cpp 
In file included from ./boost_1.84.0/boost/math/special_functions/beta.hpp:1721,
                 from boost.cpp:1:
./boost_1.84.0/boost/math/special_functions/detail/ibeta_inverse.hpp: In instantiation of ‘boost::math::detail::temme_root_finder<T>::temme_root_finder(T, T) [with T = long double]’:
./boost_1.84.0/boost/math/special_functions/detail/ibeta_inverse.hpp:304:7:   required from ‘T boost::math::detail::temme_method_2_ibeta_inverse(T, T, T, T, T, const Policy&) [with T = long double; Policy = boost::math::policies::policy<boost::math::policies::promote_float<false>, boost::math::policies::promote_double<false>, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy>]’
./boost_1.84.0/boost/math/special_functions/detail/ibeta_inverse.hpp:615:48:   required from ‘T boost::math::detail::ibeta_inv_imp(T, T, T, T, const Policy&, T*) [with T = long double; Policy = boost::math::policies::policy<boost::math::policies::promote_float<false>, boost::math::policies::promote_double<false>, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy>]’
./boost_1.84.0/boost/math/special_functions/detail/ibeta_inverse.hpp:992:30:   required from ‘boost::math::tools::promote_args_t<T1, T2, T3, T4> boost::math::ibeta_inv(T1, T2, T3, T4*, const Policy&) [with T1 = double; T2 = double; T3 = double; T4 = double; Policy = boost::math::policies::policy<boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy, boost::math::policies::default_policy>; boost::math::tools::promote_args_t<T1, T2, T3, T4> = double]’
./boost_1.84.0/boost/math/special_functions/detail/ibeta_inverse.hpp:1015:20:   required from ‘boost::math::tools::promote_args_t<RT1, RT2, A> boost::math::ibeta_inv(RT1, RT2, RT3) [with RT1 = double; RT2 = double; RT3 = double; boost::math::tools::promote_args_t<RT1, RT2, A> = double]’
boost.cpp:7:40:   required from here
./boost_1.84.0/boost/math/special_functions/detail/ibeta_inverse.hpp:29:15: warning: unused variable ‘x_extrema’ [-Wunused-variable]
   29 |       const T x_extrema = 1 / (1 + a);

Versions:

$ g++ --version
g++ (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Boost 1.84.0

[SteveBronder]

I think this can just be fixed by putting an ifdef around the assert code in #1004

#ifndef BOOST_DISABLE_ASSERTS
      const T x_extrema = 1 / (1 + a);
      BOOST_MATH_ASSERT(0 < x_extrema && x_extrema < 1);
#endif

[jzmaddock]

Fixed in develop.