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/*
**************************************************************
* C++ Mathematical Expression Toolkit Library *
* *
* Simple Example 16 *
* Author: Arash Partow (1999-2024) *
* URL: https://www.partow.net/programming/exprtk/index.html *
* *
* Copyright notice: *
* Free use of the Mathematical Expression Toolkit Library is *
* permitted under the guidelines and in accordance with the *
* most current version of the MIT License. *
* https://www.opensource.org/licenses/MIT *
* SPDX-License-Identifier: MIT *
* *
**************************************************************
*/
#include <cstdio>
#include <cstdlib>
#include <string>
#include "exprtk.hpp"
template <typename T>
void linear_least_squares()
{
typedef exprtk::symbol_table<T> symbol_table_t;
typedef exprtk::expression<T> expression_t;
typedef exprtk::parser<T> parser_t;
const std::string linear_least_squares_program =
" if (x[] == y[]) "
" { "
" beta := (sum(x * y) - sum(x) * sum(y) / x[]) / "
" (sum(x^2) - sum(x)^2 / x[]); "
" "
" alpha := avg(y) - beta * avg(x); "
" "
" rmse := sqrt(sum((beta * x + alpha - y)^2) / y[]); "
" } "
" else "
" { "
" alpha := null; "
" beta := null; "
" rmse := null; "
" } ";
T x[] = {T( 1), T( 2), T(3), T( 4), T( 5), T(6), T( 7), T( 8), T( 9), T(10)};
T y[] = {T(8.7), T(6.8), T(6), T(5.6), T(3.8), T(3), T(2.4), T(1.7), T(0.4), T(-1)};
T alpha = T(0);
T beta = T(0);
T rmse = T(0);
symbol_table_t symbol_table;
symbol_table.add_variable("alpha", alpha);
symbol_table.add_variable("beta" , beta );
symbol_table.add_variable("rmse" , rmse );
symbol_table.add_vector ("x" , x );
symbol_table.add_vector ("y" , y );
expression_t expression;
expression.register_symbol_table(symbol_table);
parser_t parser;
parser.compile(linear_least_squares_program,expression);
expression.value();
printf("alpha: %15.12f\n", alpha);
printf("beta: %15.12f\n", beta );
printf("rmse: %15.12f\n", rmse );
printf("y = %15.12fx + %15.12f\n", beta, alpha);
}
int main()
{
linear_least_squares<double>();
return 0;
}
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