ceph/src/boost/libs/math/example/policy_ref_snip11.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 #include <iostream>
  11 using std::cout; using std::endl;
  12
  13 // Setting (approximate) precision 25 bits in a single function call using make_policy.
  14
  15 //[policy_ref_snip11
  16
  17 #include <boost/math/distributions/normal.hpp>
  18 using boost::math::normal_distribution;
  19
  20 using namespace boost::math::policies;
  21
  22 const int bits = 25; // approximate precision.
  23
  24 double q = quantile(
  25       normal_distribution<double, policy<digits2<bits> > >(),
  26       0.05); // 5% quantile.
  27
  28 //] //[/policy_ref_snip11]
  29
  30 int main()
  31 {
  32   std::streamsize p = 2 + (bits * 30103UL) / 100000UL;
  33   // Approximate number of significant decimal digits for 25 bits.
  34   cout.precision(p);
  35   cout << bits << " binary bits is approoximately equivalent to " << p << " decimal digits " << endl;
  36   cout << "quantile(normal_distribution<double, policy<digits2<25> > >(), 0.05  = "
  37      << q << endl; // -1.64485
  38 }
  39
  40 /*
  41 Output:
  42   25 binary bits is approoximately equivalent to 9 decimal digits
  43   quantile(normal_distribution<double, policy<digits2<25> > >(), 0.05  = -1.64485363
  44   */
  45