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libs/math/example/policy_ref_snip11.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!
+
+#include <iostream>
+using std::cout; using std::endl;
+
+// Setting (approximate) precision 25 bits in a single function call using make_policy.
+
+//[policy_ref_snip11
+
+#include <boost/math/distributions/normal.hpp>
+using boost::math::normal_distribution;
+
+using namespace boost::math::policies;
+
+const int bits = 25; // approximate precision.
+
+double q = quantile(
+      normal_distribution<double, policy<digits2<bits> > >(), 
+      0.05); // 5% quantile.
+
+//] //[/policy_ref_snip11]
+
+int main()
+{
+  std::streamsize p = 2 + (bits * 30103UL) / 100000UL; 
+  // Approximate number of significant decimal digits for 25 bits.
+  cout.precision(p); 
+  cout << bits << " binary bits is approoximately equivalent to " << p << " decimal digits " << endl;
+  cout << "quantile(normal_distribution<double, policy<digits2<25> > >(), 0.05  = "
+     << q << endl; // -1.64485
+}
+
+/*
+Output:
+  25 binary bits is approoximately equivalent to 9 decimal digits 
+  quantile(normal_distribution<double, policy<digits2<25> > >(), 0.05  = -1.64485363
+  */
+