exprtk_gnuplot_multi.cpp

/*
 **************************************************************
 * C++ Mathematical Expression Toolkit Library *
 * *
 * ExprTk GNUPlot Multi-Curve Example *
 * 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 <iostream>
#include <string>
#include <fstream>
#include <iomanip>

#include "exprtk.hpp"


class exprtk_gnuplot_fx;

class exprtk_fx_curve
{
public:

 friend class exprtk_gnuplot_fx;

 exprtk_fx_curve& set_title(const std::string& title)
 {
 title_ = title;
 return *this;
 }

 exprtk_fx_curve& set_domain(const double min_x, const double max_x)
 {
 min_x_ = min_x;
 max_x_ = max_x;
 return *this;
 }

 exprtk_fx_curve& set_expression(const std::string& expression)
 {
 expression_ = expression;
 return *this;
 }

private:

 std::string title_;
 std::string expression_;
 double min_x_;
 double max_x_;
 double min_y_;
 double max_y_;
};

class exprtk_gnuplot_fx
{
public:

 bool plot()
 {
 for (std::size_t i = 0; i < curve_list_.size(); ++i)
 {
 if (!generate_data(i,curve_list_[i]))
 return false;
 }

 return generate_gp_script();
 }

 exprtk_gnuplot_fx& add_curve(const exprtk_fx_curve& curve)
 {
 curve_list_.push_back(curve);
 return *this;
 }

private:

 bool generate_gp_script()
 {
 std::ofstream stream("plot.gp");

 if (!stream)
 {
 return false;
 }

 double min_x = +std::numeric_limits<double>::max();
 double max_x = -std::numeric_limits<double>::max();
 double min_y = +std::numeric_limits<double>::max();
 double max_y = -std::numeric_limits<double>::max();

 for (std::size_t i = 0; i < curve_list_.size(); ++i)
 {
 exprtk_fx_curve& curve = curve_list_[i];

 if (curve.min_x_ < min_x) min_x = curve.min_x_;
 if (curve.max_x_ > max_x) max_x = curve.max_x_;
 if (curve.min_y_ < min_y) min_y = curve.min_y_;
 if (curve.max_y_ > max_y) max_y = curve.max_y_;
 }

 stream << "set term png\n";
 stream << "set output 'plot.png'\n";
 stream << "set xrange[" << min_x << ":" << max_x <<"]\n";
 stream << "set yrange[" << min_y << ":" << max_y <<"]\n";
 stream << "set xzeroaxis\n";
 stream << "set yzeroaxis\n";
 stream << "plot \\\n";

 for (std::size_t i = 0; i < curve_list_.size(); ++i)
 {
 stream << "'data.dat" << i << "' using 1:2:(1.0) smooth unique title '" << curve_list_[i].title_;
 stream << (((i + 1) < curve_list_.size()) ? "',\\\n" : "'\n");
 }

 return true;
 }

 bool generate_data(const std::size_t index, exprtk_fx_curve& curve)
 {
 typedef exprtk::symbol_table<double> symbol_table_t;
 typedef exprtk::expression<double> expression_t;
 typedef exprtk::parser<double> parser_t;

 double x = 0.0;

 symbol_table_t symbol_table;
 symbol_table.add_constants();
 symbol_table.add_variable("x",x);

 expression_t expression;
 expression.register_symbol_table(symbol_table);

 parser_t parser;

 if (!parser.compile(curve.expression_,expression))
 {
 return false;
 }

 const std::string file_name = std::string("data.dat") + (char)('0' + index);

 std::ofstream stream(file_name.c_str());

 if (!stream)
 {
 return false;
 }

 curve.min_y_ = +std::numeric_limits<double>::max();
 curve.max_y_ = -std::numeric_limits<double>::max();

 stream << std::setprecision(10);

 const double increment = std::min(0.00005,std::abs(curve.max_x_ - curve.min_x_) / 1000.0);

 for (x = curve.min_x_; x <= curve.max_x_; x += increment)
 {
 const double y = expression.value();

 if (y < curve.min_y_) curve.min_y_ = y;
 else if (y > curve.max_y_) curve.max_y_ = y;

 stream << x << "\t" << y << "\n";
 }

 const double diff_y = std::abs(curve.max_y_ - curve.min_y_);
 const double perc7_5 = diff_y * 0.075; //7.5%

 curve.min_y_ -= perc7_5;
 curve.max_y_ += perc7_5;

 return true;
 }

 std::deque<exprtk_fx_curve> curve_list_;
};

int main()
{
 exprtk_gnuplot_fx plotter;

 plotter
 .add_curve(
 exprtk_fx_curve()
 .set_expression("sin(2 * pi * x) + cos(x / 2 * pi)")
 .set_domain(-5,+5)
 .set_title("ExprTk Curve 1"))

 .add_curve(
 exprtk_fx_curve()
 .set_expression("clamp(-1.0,sin(2 * pi * x) + cos(x / 2 * pi),+1.0)")
 .set_domain(-5,+5)
 .set_title("ExprTk Curve 2"));

 plotter.plot();

 return 0;
}


/*
 Build and Run:
 1. c++ -pedantic-errors -Wall -Wextra -Werror -Wno-long-long -O3 -DNDEBUG -o exprtk_gnuplot_multi exprtk_gnuplot_multi.cpp -lstdc++
 2. ./exprtk_gnuplot_multi
 3. gnuplot plot.gp
*/