- #1

Pauly Man

- 128

- 0

I was wondering if anyone could help me with this code. I have sucessfully created a program in visual basic that can run a runge-kutta method. However I want to create one in c++, maybe eventually turn it into a .dll when i work out how to create and use them.

Here is the code:

Code:

```
// Runge-Kutta.cpp
//--------------------------------------------------
//A Runge-Kutta Method for solving Differential Equations
//of the form y'=f(x,y) ; y(x0)=y0
//--------------------------------------------------
#include <iostream>
#include <iomanip>
using namespace std;
//Define constants
#define X0 0
#define Y0 0
#define H 0.2
#define N 5
//Define Functions
double f(double x, double y);
double runge(double x, double y);
//Main Function
int main(double x, double y)
{
cout<<"\t*** Euler Method ***"
<<"\n\n";
cout<<" "
<<setw(12)<<"x"<<setw(12)<<"\ty"
<<"\n"
<<"\t------------------------------"
<<"\n";
y=Y0;
for(int i=0;i<=5;i++)
{
x=X0+(i*H);
y=runge(x,y);
cout<<left<<setw(6)<<i<<"|"
<<setprecision(4)<<left<<setw(8)<<"\t"<<x
<<setprecision(4)<<left<<setw(8)<<"\t"<<y;
cout<<"\n\n";
}
cout<<"\n\n";
return 0;
}
double runge(double x, double y)
{
double K1 = (H * f(x,y));
double K2 = (H * f((x + 1 / 2 * H), (y + 1 / 2 * K1)));
double K3 = (H * f((x + 1 / 2 * H), (y + 1 / 2 * K2)));
double K4 = (H * f((x + H), (y + K3)));
double runge = (y + (1 / 6) * (K1 + 2 * K2 + 2 * K3 + K4));
return runge;
}
double f(double x, double y)
{
double f = x+y;
return f;
}
```

It is supposed to print out a table, with the x values in one column, and y values in the other. Each successive iteration is in a new row of the table.

So far so good, the code creates the table fine.

I created a similiar program to run a Euler method, and it works just fine. But in the Runge-Kutta it just prints the y values as zero. I must have done something wrong somewhere.