Plot ChFunction objects in Matlab (demo_MTLB_functions_plot.cpp)

Entry level demo about how to use Matlab(TM) and the MATLAB module to plot Chrono::Engine objects of the chrono::ChFunction class.

// =============================================================================
// PROJECT CHRONO - http://projectchrono.org
//
// Copyright (c) 2014 projectchrono.org
// All rights reserved.
//
// Use of this source code is governed by a BSD-style license that can be found
// in the LICENSE file at the top level of the distribution and at
// http://projectchrono.org/license-chrono.txt.
//
// =============================================================================
// Authors: Alessandro Tasora
// =============================================================================
// Demo code for using the ChFunction objects for specifying functions y=f(t)
// and calling Matlab from Chrono (in particular, using Matlab to plot data)
// =============================================================================
 
#include "chrono/motion_functions/ChFunction.h"
#include "chrono_matlab/ChMatlabEngine.h"
 
// Use the namespace of Chrono
 
using namespace chrono;
 
int main(int argc, char* argv[]) {
    GetLog() << "Copyright (c) 2017 projectchrono.org\nChrono version: " << CHRONO_VERSION << "\n\n";
 
    // Better put the Matlab stuff inside a try{}, since it may throw exception if
    // the engine is not started (because Matlab not properly installed)
    try {
        GetLog() << "PERFORM TESTS OF MATLAB<->CHRONOENGINE INTERACTION\n\n";
        GetLog() << "(please wait few seconds: Matlab engine must be loaded)\n\n";
 
        // This is the object that you can use to access the Matlab engine.
        // As soon as created, it loads the Matlab engine (if troubles happen, it
        // throws exception).
        ChMatlabEngine matlab_engine;
 
        //
        // EXAMPLE 1: create a ramp ChFunction, set properties, evaluate it.
        //
 
        GetLog() << "==== Test 1...\n\n";
 
        ChFunction_Ramp f_ramp;
 
        f_ramp.Set_ang(0.1);  // set angular coefficient;
        f_ramp.Set_y0(0.4);   // set y value for x=0;
 
        // Evaluate y=f(x) function at a given x value, using Get_y() :
        double y = f_ramp.Get_y(10);
        // Evaluate derivative df(x)/dx at a given x value, using Get_y_dx() :
        double ydx = f_ramp.Get_y_dx(10);
 
        GetLog() << "   ChFunction_Ramp at x=0: y=" << y << "  dy/dx=" << ydx << "\n\n";
 
        //
        // EXAMPLE 2: plot a sine ChFunction
        //
 
        GetLog() << "==== Test 2...\n\n";
 
        ChFunction_Sine f_sine;
 
        f_sine.Set_amp(2);     // set amplitude;
        f_sine.Set_freq(0.9);  // set frequency;
 
        // Evaluate y=f(x) function along 100 x points:
        ChMatrixDynamic<> x_array(100, 1);
        ChMatrixDynamic<> y_array(100, 1);
        ChMatrixDynamic<> ydx_array(100, 1);
        ChMatrixDynamic<> ydxdx_array(100, 1);
        for (int i = 0; i < 100; i++) {
            double x = (double)i / 50.0;
            x_array(i) = x;
            y_array(i) = f_sine.Get_y(x);
            ydx_array(i) = f_sine.Get_y_dx(x);
            ydxdx_array(i) = f_sine.Get_y_dxdx(x);
        }
 
        // Send resulting vectors of values to Matlab
        matlab_engine.PutVariable(x_array, "x_array");
        matlab_engine.PutVariable(y_array, "y_array");
        matlab_engine.PutVariable(ydx_array, "ydx_array");
        matlab_engine.PutVariable(ydxdx_array, "ydxdx_array");
 
        // Plot with Matlab 'plot' command
        matlab_engine.Eval("figure;  plot(x_array,y_array,'k');");
        matlab_engine.Eval("hold on; plot(x_array,ydx_array,'g');");
        matlab_engine.Eval("grid on; plot(x_array,ydxdx_array,'r');");
        matlab_engine.Eval("legend ('y','dy/dx','ddy/dxdx');");
 
        GetLog() << "Press a key to finish... \n";
        getchar();  // pause until key..
    } catch (ChException mex) {
        GetLog() << mex.what();  // Print error on console, if Matlab did not start.
    }
 
    return 0;
}