struna.cc
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// Model struna.cc
// Problem: kmitani struny (SKRIPTA strana 42)
// reseni parcialni dif. rovnice, metoda primek
// (c) Petr Peringer, 1997
#include "simlib.h"
// parameters of simulation:
const double Print_Step = 0.001; // perioda vzorkování
const double Simul_Time = 0.05; // doba simulace
// equation
class Struna {
const unsigned N; // pocet useku
const double l; // delka
const double a; // koeficient (napeti ve strune ???)
const double b; // pocatecni vychylka uprostred struny
class Point : public aContiBlock {
Integrator v; // y'
Integrator y; // y
public:
Point() : v(), y(v) {}
double Value() { return y.Value(); }
void Set(Input i, double y0) {
v.SetInput(i);
y.Init(y0);
}
};
Point *y; // uzlove body
public:
Struna(unsigned _N, double _l, double _a, double _b) :
N(_N), l(_l), a(_a), b(_b) {
// konstrukce modelu:
y = new Point[N+1];
const double dx = l/N; // delka useku
const double adx2 = a/(dx*dx);
double xi = dx;
for(int i=1; i<N; i++) {
y[i].Set( adx2 * (y[i+1] - 2*y[i] + y[i-1]), // nastaveni vstupu
b * (-4/(l*l) * xi*xi + 4/l * xi)); // pocatecni podminka
xi += dx;
}
}
double GetX(unsigned i) { return (i<=N) ? i*l/N : 0.0; }
double GetY(unsigned i) { return (i<=N) ? y[i].Value() : 0.0; }
unsigned GetN() { return N; }
};
Struna s(100, 1, 1e3, 0.01);
void Sample() {
Print("# x y \n");
for(int i=0; i<=s.GetN(); i++)
Print("%-8g %g \n", s.GetX(i), s.GetY(i) );
Print("\n");
}
Sampler S(Sample, Print_Step);
int main() {
SetOutput("struna.dat"); // output file
_Print("# Struna \n");
Init(0, Simul_Time); // inicializace experimentu
Run(); // simulace
}
//
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![[results]](struna.png)
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