91 lines
3.4 KiB
C++
91 lines
3.4 KiB
C++
/*
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**************************************************************
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* C++ Mathematical Expression Toolkit Library *
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* *
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* Simple Example 16 *
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* Author: Arash Partow (1999-2024) *
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* URL: https://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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* https://www.opensource.org/licenses/MIT *
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* SPDX-License-Identifier: MIT *
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* *
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**************************************************************
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*/
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#include <cstdio>
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#include <cstdlib>
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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 linear_least_squares()
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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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const std::string linear_least_squares_program =
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" if (x[] == y[]) "
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" { "
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" var mean_x := avg(x); "
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" var mean_y := avg(y); "
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" "
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" beta := sum((x - mean_x) * (y - mean_y)) / "
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" sum((x - mean_x)^2); "
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" "
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" alpha := mean_y - beta * mean_x; "
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" "
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" rmse := sqrt(sum((beta * x + alpha - y)^2) / y[]); "
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" } "
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" else "
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" { "
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" alpha := null; "
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" beta := null; "
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" rmse := null; "
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" } ";
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T x[] = { T(1.0), T(2.0), T(3.0), T(4.0), T(5.0), T(6.0), T(7.0), T(8.0), T(9.0), T(10) };
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T y[] = { T(8.7), T(6.8), T(6.0), T(5.6), T(3.8), T(3.0), T(2.4), T(1.7), T(0.4), T(-1) };
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T alpha = T(0);
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T beta = T(0);
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T rmse = T(0);
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symbol_table_t symbol_table;
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symbol_table.add_variable("alpha", alpha);
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symbol_table.add_variable("beta" , beta );
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symbol_table.add_variable("rmse" , rmse );
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symbol_table.add_vector ("x" , x );
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symbol_table.add_vector ("y" , y );
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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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if (!parser.compile(linear_least_squares_program,expression))
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{
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printf("error: %s\n",parser.error().c_str());
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return;
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}
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expression.value();
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printf("alpha: %15.12f\n", alpha);
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printf("beta: %15.12f\n", beta );
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printf("rmse: %15.12f\n", rmse );
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printf("y = %15.12fx + %15.12f\n", beta, alpha);
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}
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int main()
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{
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linear_least_squares<double>();
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return 0;
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}
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