/*

**************************************************************

* C++ Mathematical Expression Toolkit Library *

* *

* Simple Example 13 *

* Author: Arash Partow (1999-2025) *

* 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 <ctime>

#include <string>

#include "exprtk.hpp"

template <typename T>

void savitzky_golay_filter()

{

typedef exprtk::symbol_table<T> symbol_table_t;

typedef exprtk::expression<T> expression_t;

typedef exprtk::parser<T> parser_t;

const std::string sgfilter_program =

" var weight[9] := "

" { "

" -21, 14, 39, "

" 54, 59, 54, "

" 39, 14, -21 "

" }; "

" "

" if (v_in[] >= weight[]) "

" { "

" const var lower_bound := trunc(weight[] / 2); "

" const var upper_bound := v_in[] - lower_bound; "

" "

" v_out := 0; "

" "

" for (var i := lower_bound; i < upper_bound; i += 1) "

" { "

" for (var j := -lower_bound; j <= lower_bound; j += 1) "

" { "

" v_out[i] += weight[j + lower_bound] * v_in[i + j]; "

" }; "

" }; "

" "

" v_out /= sum(weight); "

" } ";

const std::size_t n = 1024;

std::vector<T> v_in;

std::vector<T> v_out;

const T pi = T(3.141592653589793238462643383279502);

srand(static_cast<unsigned int>(time(0)));

// Generate a signal with noise.

for (T t = T(-5); t <= T(+5); t += T(10.0 / n))

{

const T noise = T(0.5 * (rand() / (RAND_MAX + 1.0) - 0.5));

v_in.push_back(sin(2.0 * pi * t) + noise);

}

v_out.resize(v_in.size());

symbol_table_t symbol_table;

symbol_table.add_vector("v_in" , v_in );

symbol_table.add_vector("v_out", v_out);

expression_t expression;

expression.register_symbol_table(symbol_table);

parser_t parser;

parser.compile(sgfilter_program,expression);

expression.value();

for (std::size_t i = 0; i < v_out.size(); ++i)

{

printf("%10.6f\t%10.6f\n", v_in[i], v_out[i]);

}

}

int main()

{

savitzky_golay_filter<double>();

return 0;

}