exprtk_simple_example_10.cpp File Reference

#include <cmath>
#include <cstdio>
#include <string>
#include "exprtk.hpp"

Include dependency graph for exprtk_simple_example_10.cpp:

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Functions
template<typename T >
void	newton_sqrt ()
int	main ()

Function Documentation

main()

int main

(

)

Definition at line 93 of file exprtk_simple_example_10.cpp.

{
   newton_sqrt<double>();
   return 0;
}

newton_sqrt()

template<typename T >

void newton_sqrt

(

)

Definition at line 28 of file exprtk_simple_example_10.cpp.

{
   typedef exprtk::symbol_table<T>         symbol_table_t;
   typedef exprtk::expression<T>           expression_t;
   typedef exprtk::parser<T>               parser_t;
   typedef exprtk::function_compositor<T>  compositor_t;
   typedef typename compositor_t::function function_t;
 
   T x = T(0);
 
   symbol_table_t symbol_table;
 
   symbol_table.add_constants();
   symbol_table.add_variable("x",x);
 
   compositor_t compositor(symbol_table);
 
   compositor.add(
      function_t("newton_sqrt")
      .var("x")
      .expression
      (
         " switch                                                   "
         " {                                                        "
         "    case x < 0  : null;                                   "
         "    case x == 0 : 0;                                      "
         "    case x == 1 : 1;                                      "
         "    default:                                              "
         "    {                                                     "
         "       var z := 100;                                      "
         "       var sqrt_x := x / 2;                               "
         "       repeat                                             "
         "          if (equal(sqrt_x^2, x))                         "
         "             break[sqrt_x];                               "
         "          else                                            "
         "             sqrt_x := (1 / 2) * (sqrt_x + (x / sqrt_x)); "
         "       until ((z -= 1) <= 0);                             "
         "    };                                                    "
         " }                                                        "
      ));
 
   const std::string expression_str = "newton_sqrt(x)";
 
   expression_t expression;
   expression.register_symbol_table(symbol_table);
 
   parser_t parser;
   parser.compile(expression_str,expression);
 
   for (std::size_t i = 0; i < 1000; ++i)
   {
      x = static_cast<T>(i);
 
      const T result = expression.value();
      const T real   = std::sqrt(x);
      const T error  = std::abs(result - real);
 
      printf("sqrt(%03d) - Result: %15.13f\tReal: %15.13f\tError: %18.16f\n",
             static_cast<unsigned int>(i),
             result,
             real,
             error);
   }
}