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// -*- mode: C++; c-indent-level: 4; c-basic-offset: 4; tab-width: 8; -*-
//
// Example of a planetary motion solver with interactive console
//
// Copyright (C) 2009 Dirk Eddelbuettel
// Copyright (C) 2010 - 2017 Dirk Eddelbuettel and Romain Francois
// Copyright (C) 2017 Dirk Eddelbuettel, Romain Francois and Łukasz Łaniewski-Wołłk
//
// GPL'ed
#include <RInside.h> // for the embedded R via RInside
class Wrapper;
// A planet.
struct Planet {
double x,y;
double m;
double vx, vy;
};
// A gravity simulator
class Solver {
typedef std::vector<Planet> Planets;
Planets tab;
double dt;
double G;
void Iteration() {
for (Planets::iterator a=tab.begin(); a != tab.end(); a++) {
for (Planets::iterator b=tab.begin(); b != a; b++) {
double x = a->x - b->x;
double y = a->y - b->y;
double r = sqrt(x*x + y*y);
double f = a->m * b->m * G / (r*r+1);
double fx = f * x/r;
double fy = f * y/r;
a->vx -= dt * fx / a->m;
a->vy -= dt * fy / a->m;
b->vx += dt * fx / b->m;
b->vy += dt * fy / b->m;
}
}
for (Planets::iterator a=tab.begin(); a != tab.end(); a++) {
a->x += dt * a->vx;
a->y += dt * a->vy;
}
}
public:
Solver(int n): tab(n), dt(1.0e-4), G(1.0) {
double v=0;
for (Planets::iterator a=tab.begin(); a != tab.end(); a++) {
a->x = sin(v);
a->y = cos(v);
a->m = 1;
v += 3.0/n;
}
}
void Iterate(int n) {
for (int i=0;i<n;i++) Iteration();
}
friend class Wrapper;
};
// A nice wrapper for the solver
class Wrapper {
Solver * s;
public:
Wrapper(Solver * s_) : s(s_) {}
Rcpp::DataFrame getData() {
Rcpp::NumericVector x,y,m,vx,vy;
for (Solver::Planets::iterator a=s->tab.begin(); a != s->tab.end(); a++) {
x.push_back( a->x);
y.push_back( a->y);
m.push_back( a->m);
vx.push_back(a->vx);
vy.push_back(a->vy);
}
return Rcpp::DataFrame::create(Rcpp::Named("x") = x,
Rcpp::Named("y") = y,
Rcpp::Named("mass") = m,
Rcpp::Named("Vx") = vx,
Rcpp::Named("Vy") = vy);
}
void setData(Rcpp::DataFrame tab) {
if ((size_t)tab.nrows() != s->tab.size()) {
return;
}
Rcpp::NumericVector x = tab["x"];
Rcpp::NumericVector y = tab["y"];
Rcpp::NumericVector m = tab["mass"];
Rcpp::NumericVector vx = tab["Vy"];
Rcpp::NumericVector vy = tab["Vy"];
for (int i=0;i<tab.nrows();i++) {
s->tab[i].x = x[i];
s->tab[i].y = y[i];
s->tab[i].m = m[i];
s->tab[i].vx = vx[i];
s->tab[i].vy = vy[i];
}
}
double& G() {
return s->G;
}
double& dt() {
return s->dt;
}
};
// The function which is called when running Solver$...
SEXP Dollar(Rcpp::XPtr<Wrapper> obj, std::string name) {
if (name == "data") {
return obj->getData();
} else if (name == "G") {
return Rcpp::NumericVector(1,obj->G());
} else if (name == "dt") {
return Rcpp::NumericVector(1,obj->dt());
} else {
return NULL;
}
}
// The function which is called when assigning to Solver$...
Rcpp::XPtr<Wrapper> DollarAssign(Rcpp::XPtr<Wrapper> obj, std::string name, SEXP v) {
if (name == "data") {
obj->setData(v);
} else if (name == "G") {
obj->G() = Rcpp::NumericVector(v)[0];
} else if (name == "dt") {
obj->dt() = Rcpp::NumericVector(v)[0];
}
return obj;
}
// The function listing the elements of Solver
Rcpp::CharacterVector Names(Rcpp::XPtr<Wrapper> obj) {
Rcpp::CharacterVector ret;
ret.push_back("data");
ret.push_back("G");
ret.push_back("dt");
return ret;
}
int main(int argc, char *argv[]) {
Solver S(70); // Creating the gravity simulator
RInside R(argc, argv, false, false, true); // Create an embedded R instance
Rcpp::XPtr<Wrapper> wr(new Wrapper(&S)); // Wrapping the solver
wr.attr("class") = "Solver";
R["Solver"] = wr; // Adding the wrapped solver
R["$.Solver"] = Rcpp::InternalFunction(& Dollar); // Adding the functions
R["$<-.Solver"] = Rcpp::InternalFunction(& DollarAssign);
R["names.Solver"] = Rcpp::InternalFunction(& Names);
char type;
do {
std::cout << "Want to go interactive? [y/n]";
std::cin >> type;
} while ( !std::cin.fail() && type!='y' && type!='n' );
if (type == 'y') { // Running an interactive R session
std::cout << "Running an interactive R session. You can explore (and modify) the data in the 'Solver' object." << std::endl;
std::cout << "[ You can finish the with Ctrl+D ]" << std::endl;
R.parseEval("options(prompt = 'R console > ')");
R.parseEval("X11()");
R.repl() ;
std::cout << "Finishing the interactive mode" << std::endl;
R.parseEval("dev.off()");
}
R.parseEval("X11()");
for (int i=0;i<2000;i++) { // Running the some 200'000 iterations in non-interactive mode
S.Iterate(100);
R.parseEval("P = Solver$data;");
R.parseEval("plot(P$x,P$y,cex=P$mass,asp=1,xlim=c(-5,5),ylim=c(-5,5),xlab='X',ylab='Y')");
}
exit(0);
}
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