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using variables outside the function

Tcm (3)
In the the function runge4 two of the things it calculates are k1[i=0] and y[i=0]. Is there any way to use those in the main such that dist = y[0]/k1[0] because there are local variables? and each time the loop calculates new k[0],y[0] use those as a new estimate of the step in main.

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  /

#define N 2                     
//#define dist 0.1                
#define MAX 30.0                
 
FILE *output;                  

void runge4(double x, double y[], double step); 

double f(double x, double y[], int i);          

main()
{
double t, y[N];
double dist;
 
output=fopen("osc.dat", "w");                   

y[0]=1.0;                                       
y[1]=0.0;                                      
fprintf(output, "0\t%f\n", y[0]);

int j=1;
double s=0;
while (dist*j<=MAX)
{
	t= j*dist;
	runge4(t,y,dist);
	j++;
	if (y[0]<0)
		break;
	
	fprintf(output, "%f\t%f\n", t, y[0]);

}
fclose(output);
}

void runge4(double x, double y[], double step)
{
double h=step/2.0,                      
        t1[N], t2[N], t3[N],            
        k1[N], k2[N], k3[N],k4[N];      
int i;
 
for (i=0;i<N;i++) t1[i]=y[i]+0.5*(k1[i]=step*f(x, y, i));
for (i=0;i<N;i++) t2[i]=y[i]+0.5*(k2[i]=step*f(x+h, t1, i));
for (i=0;i<N;i++) t3[i]=y[i]+    (k3[i]=step*f(x+h, t2, i));
for (i=0;i<N;i++) k4[i]=                step*f(x+step, t3, i);

for (i=0;i<N;i++) y[i]+=(k1[i]+2*k2[i]+2*k3[i]+k4[i])/6.0;
}

double  f(double x, double y[], int i)
{
............       
}
Last edited on
mitchellotis (2)
Id take a guess that you could try creating a variable for them in main and returning them at the end of the function!
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