ceph/src/boost/libs/math/example/policy_ref_snip12.cpp

   1 //  Copyright John Maddock 2007.
   2 //  Copyright Paul A. Bristow 2010
   3 //  Use, modification and distribution are subject to the
   4 //  Boost Software License, Version 1.0. (See accompanying file
   5 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6
   7 // Note that this file contains quickbook mark-up as well as code
   8 // and comments, don't change any of the special comment mark-ups!
   9
  10 // Define tgamma function with a no overflow policy
  11 // into a specific namespace-scope.
  12
  13 #include <iostream>
  14 using std::cout; using std::endl;
  15
  16 //[policy_ref_snip12
  17
  18 #include <boost/math/special_functions/gamma.hpp>
  19 //using boost::math::tgamma;
  20 // Need not declare using boost::math::tgamma here,
  21 // because will define tgamma in myspace using macro below.
  22
  23 namespace myspace
  24 {
  25   using namespace boost::math::policies;
  26
  27   // Define a policy that does not throw on overflow:
  28   typedef policy<overflow_error<errno_on_error> > my_policy;
  29
  30   // Define the special functions in this scope to use the policy:
  31   BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS(my_policy)
  32 }
  33
  34 // Now we can use myspace::tgamma etc.
  35 // They will automatically use "my_policy":
  36 //
  37 double t = myspace::tgamma(30.0); // Will *not* throw on overflow,
  38 // despite the large value of factorial 30 = 265252859812191058636308480000000
  39 // unlike default policy boost::math::tgamma;
  40
  41 //]
  42
  43 int main()
  44 {
  45    cout << "myspace::tgamma(30.0) = " << t << endl;
  46 }
  47
  48 /*
  49
  50 Output:
  51
  52 myspace::tgamma(30.0) = 8.84176e+030
  53
  54 */
  55