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91 lines
3.1 KiB
C++
91 lines
3.1 KiB
C++
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/*
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**************************************************************
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* C++ Mathematical Expression Toolkit Library *
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* *
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* Simple Example 10 *
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* Author: Arash Partow (1999-2017) *
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* URL: http://www.partow.net/programming/exprtk/index.html *
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* *
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* Copyright notice: *
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* Free use of the Mathematical Expression Toolkit Library is *
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* permitted under the guidelines and in accordance with the *
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* most current version of the MIT License. *
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* http://www.opensource.org/licenses/MIT *
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* *
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**************************************************************
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*/
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#include <cmath>
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#include <cstdio>
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#include <string>
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#include "exprtk.hpp"
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template <typename T>
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void newton_sqrt()
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{
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typedef exprtk::symbol_table<T> symbol_table_t;
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typedef exprtk::expression<T> expression_t;
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typedef exprtk::parser<T> parser_t;
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typedef exprtk::function_compositor<T> compositor_t;
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typedef typename compositor_t::function function_t;
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T x = T(0);
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symbol_table_t symbol_table;
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symbol_table.add_constants();
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symbol_table.add_variable("x",x);
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compositor_t compositor(symbol_table);
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compositor
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.add(
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function_t( // define function: newton_sqrt(x)
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"newton_sqrt",
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" switch "
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" { "
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" case x < 0 : -inf; "
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" case x == 0 : 0; "
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" case x == 1 : 1; "
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" default: "
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" ~{ "
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" var z := 100; "
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" var sqrt_x := x / 2; "
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" repeat "
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" sqrt_x := (1 / 2) * (sqrt_x + (x / sqrt_x)); "
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" if (equal(sqrt_x^2, x)) "
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" break[sqrt_x]; "
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" until ((z -= 1) <= 0); "
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" }; "
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" } ",
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"x"));
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std::string expression_str = "newton_sqrt(x)";
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expression_t expression;
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expression.register_symbol_table(symbol_table);
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parser_t parser;
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parser.compile(expression_str,expression);
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for (std::size_t i = 0; i < 100; ++i)
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{
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x = i;
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T result = expression.value();
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printf("sqrt(%03d) - Result: %12.10f\tReal: %12.10f\n",
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static_cast<unsigned int>(i),
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result,
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std::sqrt(x));
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}
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}
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int main()
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{
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newton_sqrt<double>();
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return 0;
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}
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