Initial commit

libs/math/example/policy_eg_8.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!
+
+#ifdef _MSC_VER
+# pragma warning (disable : 4100) // unreferenced formal parameters
+#endif
+
+#include <iostream>
+using std::cout;  using std::endl; using std::cerr;
+
+//[policy_eg_8
+
+/*`
+Suppose we want our own user-defined error handlers rather than the
+any of the default ones supplied by the library to be used.
+If we set the policy for a specific type of error to `user_error`
+then the library will call a user-supplied error handler.
+These are forward declared, but not defined in
+boost/math/policies/error_handling.hpp like this:
+
+   namespace boost{ namespace math{ namespace policies{
+
+   template <class T>
+   T user_domain_error(const char* function, const char* message, const T& val);
+   template <class T>
+   T user_pole_error(const char* function, const char* message, const T& val);
+   template <class T>
+   T user_overflow_error(const char* function, const char* message, const T& val);
+   template <class T>
+   T user_underflow_error(const char* function, const char* message, const T& val);
+   template <class T>
+   T user_denorm_error(const char* function, const char* message, const T& val);
+   template <class T>
+   T user_evaluation_error(const char* function, const char* message, const T& val);
+   template <class T, class TargetType>
+   T user_rounding_error(const char* function, const char* message, const T& val, const TargetType& t);
+   template <class T>
+   T user_indeterminate_result_error(const char* function, const char* message, const T& val);
+
+   }}} // namespaces
+
+So out first job is to include the header we want to use, and then
+provide definitions for our user-defined error handlers that we want to use.
+We only provide our special domain and pole error handlers;
+other errors like overflow and underflow use the default.
+*/
+
+#include <boost/math/special_functions.hpp>
+
+namespace boost{ namespace math
+{
+  namespace policies
+  {
+    template <class T>
+    T user_domain_error(const char* function, const char* message, const T& val)
+    { // Ignoring function, message and val for this example, perhaps unhelpfully.
+       cerr << "Domain Error!" << endl;
+       return std::numeric_limits<T>::quiet_NaN();
+    }
+
+    template <class T>
+    T user_pole_error(const char* function, const char* message, const T& val)
+    { // Ignoring function, message and val for this example, perhaps unhelpfully.
+       cerr << "Pole Error!" << endl;
+       return std::numeric_limits<T>::quiet_NaN();
+    }
+  } // namespace policies
+}} // namespace boost{ namespace math
+
+
+/*`
+Now we'll need to define a suitable policy that will call these handlers,
+and define some forwarding functions that make use of the policy:
+*/
+
+namespace mymath{
+
+using namespace boost::math::policies;
+
+typedef policy<
+   domain_error<user_error>,
+   pole_error<user_error>
+> user_error_policy;
+
+BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS(user_error_policy)
+
+} // close unnamed namespace
+
+/*`
+We now have a set of forwarding functions defined in namespace mymath
+that all look something like this:
+
+``
+template <class RealType>
+inline typename boost::math::tools::promote_args<RT>::type
+   tgamma(RT z)
+{
+   return boost::math::tgamma(z, user_error_policy());
+}
+``
+
+So that when we call `mymath::tgamma(z)` we really end up calling
+`boost::math::tgamma(z, user_error_policy())`, and any
+errors will get directed to our own error handlers.
+*/
+
+int main()
+{
+   cout << "Result of erf_inv(-10) is: "
+      << mymath::erf_inv(-10) << endl;
+   cout << "Result of tgamma(-10) is: "
+      << mymath::tgamma(-10) << endl;
+}
+
+/*`
+
+Which outputs:
+
+[pre
+  Domain Error!
+  Pole Error!
+  Result of erf_inv(-10) is: 1.#QNAN
+  Result of tgamma(-10) is: 1.#QNAN
+]
+*/
+
+//] // //[/policy_eg_8]