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libs/math/example/factorial_example.cpp

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+// TestFactorial.cpp
+//
+// Factorials and Binomial Coefficients.
+//
+// Copyright Datasim Education BV 2009-2010
+// Copyright John Maddock and 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)
+
+#include <boost/math/special_functions/factorials.hpp>
+#include <boost/math/special_functions.hpp>
+
+#include <iostream>
+using namespace std;
+
+int main()
+{
+  using namespace boost::math;
+
+  // Factorials
+  unsigned int n = 3;
+ 
+  try
+  {
+     cout << "Factorial: " << factorial<double>(n) << endl;
+
+     // Caution: You must provide a return type template value, so this will not compile
+     // unsigned int nfac = factorial(n); // could not deduce template argument for 'T'
+     // You must provide an explicit floating-point (not integer) return type.
+     // If you do provide an integer type, like this:
+     // unsigned int uintfac = factorial<unsigned int>(n);
+     // you will also get a compile error, for MSVC C2338.
+     // If you really want an integer type, you can convert from double:
+     unsigned int intfac = static_cast<unsigned int>(factorial<double>(n));
+     // this will be exact, until the result of the factorial overflows the integer type.
+
+     cout << "Unchecked factorial: " << boost::math::unchecked_factorial<float>(n) << endl;
+     // Note:
+     // unsigned int unfac = boost::math::unchecked_factorial<unsigned int>(n);
+     // also fails to compile for the same reasons.
+  } 
+  catch(exception& e)
+  {
+    cout << e.what() << endl;
+  }
+
+  // Double factorial n!!
+  try
+  {
+    //cout << "Double factorial: " << boost::math::double_factorial<unsigned>(n);
+  }
+  catch(exception& e)
+  {
+    cout << e.what() << endl;
+  }
+
+  // Rising and falling factorials
+  try
+  {
+    int i = 2; double x = 8;
+    cout << "Rising factorial: " << rising_factorial(x,i) << endl;
+    cout << "Falling factorial: " << falling_factorial(x,i) << endl;
+  }
+  catch(exception& e)
+  {
+    cout << e.what() << endl;
+  }
+
+  // Binomial coefficients
+  try
+  {
+    unsigned n = 10; unsigned k = 2;
+    // cout << "Binomial coefficient: " << boost::math::binomial_coefficient<unsigned>(n,k) << endl;
+  }
+  catch(exception& e)
+  {
+    cout << e.what() << endl;
+  }
+  return 0;
+}
+
+/*
+
+Output:
+
+  factorial_example.vcxproj -> J:\Cpp\MathToolkit\test\Math_test\Release\factorial_example.exe
+  Factorial: 6
+  Unchecked factorial: 6
+  Rising factorial: 72
+  Falling factorial: 56
+
+*/
+
+