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libs/math/example/policy_ref_snip3.cpp

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+//  Copyright John Maddock 2007.
+//  Copyright Paul A. Bristow 2010
+//  Use, modification and distribution are subject to the
+//  Boost Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+// Note that this file contains quickbook mark-up as well as code
+// and comments, don't change any of the special comment mark-ups!
+
+double some_value = 2.;
+
+//[policy_ref_snip3
+
+#include <boost/math/special_functions/gamma.hpp>
+
+using namespace boost::math::policies;
+using boost::math::tgamma;
+
+// Define a new policy *not* internally promoting RealType to double:
+typedef policy<
+      promote_double<false> 
+      > my_policy;
+      
+// Call the function, applying the new policy:
+double t1 = tgamma(some_value, my_policy());
+
+// Alternatively we could use helper function make_policy,
+// and concisely define everything at the call site:
+double t2 = tgamma(some_value, make_policy(promote_double<false>()));
+
+//] //[\policy_ref_snip3]
+
+#include <iostream>
+using std::cout;  using std::endl;
+
+int main()
+{
+   cout << "tgamma(some_value, my_policy()) = " << t1 
+     << ", tgamma(some_value, make_policy(promote_double<false>()) = " << t2 << endl;
+}