Trying to combine three codes in 1 code. Error came out

[albertaw1988]

I'm trying to solve a numerical problem. Ordinary Differential Equation and this problem have 3 methods to solve it. I've type out 3 individual method and try to combine them into 1 code. I'm using Visio studio 2005.

#include "stdafx.h"
#include "math.h"


float f1(float t,float x, float v);
float f2(float t,float x, float v);


int _tmain(int argc, _TCHAR* argv[])//Euler method
{
FILE *wPtr;
wPtr=fopen("res ults.xls","w");

float t0,x0,v0,tn,n,h ;
float k1,k2,t,x,v;

printf("Please Inset initial time, t0 = ");
scanf ("%f",&t0);
printf("Please Insert initial displacement, x0 = ");
scanf ("%f",&x0);
printf("Please insert initial velocity, v0= ");
scanf ("%f",&v0);
printf("Please insert final time,tn= ");
scanf ("%f",&tn);
printf("Please insert -1 to end the program.");
printf("\n");
printf("\nPleas e insert n value= ");
scanf ("%f",&n);

while (n!=-1)
{
printf("\nt\t\t x\t\tv\n");
h=(tn-t0)/n;
t=t0;
x=x0;
v=v0;

while(t<tn)
{
k1=h*f1(t,x,v);
k2=h*f2(t,x,v);

x=x+k1;
v=v+k2;
t=t+h;

printf("%f %f %f\n",t,x,v);
fprintf(wPtr,"% f %f %f\n",t,x,v);

}

printf("\nPleas e insert n value= ");
scanf ("%f",&n);
}

fclose(wPtr);
printf ("Thankyou for using.\n\n");

return 0;
}


float f1(float t,float x, float v)
{
return v;
}

float f2(float t, float x, float v)
{
return (0.5*cos(0.5*t)-1*x-0.5*pow(x,3)-0.4*v)/1;
}

=============== =============== =============== =============== =============== =============== =============== =============== =============== =============== =====

#include "stdafx.h"
#include "math.h"


float f1(float t,float x, float v);
float f2(float t,float x, float v);


int _tmain(int argc, _TCHAR* argv[])//Huen's method
{
FILE *wPtr;
wPtr=fopen("res ults.xls","w");

float t0,x0,v0,tn,n,h ;
float dydx11,dydx12,d ydx21,dydx22,sl ope1,slope2,t,x ,xe,ve,v;

printf("Please Inset initial time, t0 = ");
scanf ("%f",&t0);
printf("Please Insert initial displacement, x0 = ");
scanf ("%f",&x0);
printf("Please insert initial velocity, v0= ");
scanf ("%f",&v0);
printf("Please insert final time,tn= ");
scanf ("%f",&tn);
printf("Please insert -1 to end the program.");
printf("\n");
printf("\nPleas e insert n value= ");
scanf ("%f",&n);

while(n!=-1)
{

printf("\nt\t\t x\t\tv\n");
h=(tn-t0)/n;
t=t0;
x=x0;
v=v0;

while(t<tn)
{
dydx11=f1(t,x,v );
dydx12=f2(t,x,v );

xe=x+h*dydx11;
ve=v+h*dydx12;

dydx21=f1(t+h,x e,ve);
dydx22=f2(t+h,x e,ve);

slope1=(dydx11+ dydx21)/2;
slope2=(dydx12+ dydx22)/2;

x=x+h*slope1;
v=v+h*slope2;

t=t+h;

printf("%f %f %f\n",t,x,v);
fprintf(wPtr,"% f %f %f\n",t,x,v);

}
printf("\nPleas e insert n value= ");
scanf ("%f",&n);
}

fclose(wPtr);
printf ("Thankyou for using.\n\n");
return 0;
}


float f1(float t,float x, float v)
{
return v;
}

float f2(float t, float x, float v)
{
return (0.5*cos(0.5*t)-1*x-0.5*pow(x,3)-0.4*v)/1;
}


=============== =============== =============== =============== =============== =============== =============== =============== =============== =============== =====

#include "stdafx.h"
#include "math.h"


float f1(float t,float x, float v);
float f2(float t,float x, float v);


int _tmain(int argc, _TCHAR* argv[])//Range-Kutta method
{
FILE *wPtr;
wPtr=fopen("res ults.xls","w");

float t0,x0,v0,tn,n,h ;
float k11,k12,k21,k22 ,k31,k32,k41,k4 2,slope1,slope2 ,t,x,v;

printf("Please Inset initial time, t0 = ");
scanf ("%f",&t0);
printf("Please Insert initial displacement, x0 = ");
scanf ("%f",&x0);
printf("Please insert initial velocity, v0= ");
scanf ("%f",&v0);
printf("Please insert final time,tn= ");
scanf ("%f",&tn);
printf("Please insert EOF to end the program.");
printf("\n");
printf("\nPleas e insert n value= ");
scanf ("%f",&n);

while(n!=-1)
{

printf("\nt\t\t x\t\tv\n");
h=(tn-t0)/n;
t=t0;
x=x0;
v=v0;

while(t<tn)
{
k11=f1(t,x,v);
k12=f2(t,x,v);

k21=f1(t+h/2,x+k11*h/2, v+k12*h/2);
k22=f2(t+h/2,x+k11*h/2, v+k12*h/2);

k31=f1(t+h/2,x+k21*h/2, v+k22*h/2);
k32=f2(t+h/2,x+k21*h/2, v+k22*h/2);

k41=f1(t+h, x+k31*h, v+k32*h);
k42=f2(t+h, x+k31*h, v+k32*h);

slope1=(k11+2*k 21+2*k31+k41)/6;
slope2=(k12+2*k 22+2*k32+k42)/6;

x=x+h*slope1;
v=v+h*slope2;

t=t+h;

printf("%f %f %f\n",t,x,v);
fprintf(wPtr,"% f %f %f\n",t,x,v);

}
printf("\nPleas e insert n value= ");
scanf ("%f",&n);
}

fclose(wPtr);
printf ("Thankyou for using.\n\n");
return 0;
}


float f1(float t,float x, float v)
{
return v;
}

float f2(float t, float x, float v)
{
return (0.5*cos(0.5*t)-1*x-0.5*pow(x,3)-0.4*v)/1;
}

=============== =============== =============== ===========
and here's my combined code:

#include "stdafx.h"
#include "math.h"

float dxdt(float t, float x, float v);
float dvdt(float t, float x, float v);

FILE *wEuler;
FILE *wHuen;
FILE *wRK;

float Euler(float t0, float x0, float v0, float tn,int n )
{

float t,x,v,h;
float k1,k2;

printf("\nt\t\t x\t\tv\n");
fprintf(wEuler, "\nt\tx\tv\ n");

h=(tn-t0)/n;
t=t0;
x=x0;
v=v0;

while(t<tn)
{
k1=h*dxdt(t,x,v );
k2=h*dvdt(t,x,v );

x=x+k1;
v=v+k2;
t=t+h;

printf("%f %f %f\n",t,x,v);
fprintf(wEuler, "%f %f %f\n",t,x,v);

}

return 0;
}

float Huen(float t0, float x0, float v0, float tn,int n )
{

float t,x,v,h;
float dydx11,dydx12,d ydx21,dydx22,sl ope1,slope2,xe, ve;

printf("\nt\t\t x\t\tv\n");
fprintf(wHuen," \n\nt\tx\tv\n") ;

h=(tn-t0)/n;
t=t0;
x=x0;
v=v0;

while(t<tn)
{
dydx11=dxdt(t,x ,v);
dydx12=dvdt(t,x ,v);

xe=x+h*dydx11;
ve=v+h*dydx12;

dydx21=dxdt(t+h ,xe,ve);
dydx22=dvdt(t+h ,xe,ve);

slope1=(dydx11+ dydx21)/2;
slope2=(dydx12+ dydx22)/2;

x=x+h*slope1;
v=v+h*slope2;

t=t+h;

printf("%f %f %f\n",t,x,v);
fprintf(wHuen," %f %f %f\n",t,x,v);

}

return 0;
}

float RK(float t0, float x0, float v0, float tn,int n )
{

float t,x,v,h;
float k11,k12,k21,k22 ,k31,k32,k41,k4 2,s1,s2;

printf("\nt\t\t x\t\tv\n");
fprintf(wRK,"\n t\tx\tv\n");

h=(tn-t0)/n;
t=t0;
x=x0;
v=v0;

while(t<tn)
{
k11=dxdt(t,x,v) ;
k12=dvdt(t,x,v) ;

k21=dxdt(t+h/2,x+k11*h/2, v+k12*h/2);
k22=dvdt(t+h/2,x+k11*h/2, v+k12*h/2);

k31=dxdt(t+h/2,x+k21*h/2, v+k22*h/2);
k32=dvdt(t+h/2,x+k21*h/2, v+k22*h/2);

k41=dxdt(t+h, x+k31*h, v+k32*h);
k42=dvdt(t+h, x+k31*h, v+k32*h);

s1=(k11+2*k21+2 *k31+k41)/6;
s2=(k12+2*k22+2 *k32+k42)/6;

x=x+h*s1;
v=v+h*s2;

t=t+h;

printf("%f %f %f\n",t,x,v);
fprintf(wRK,"%f %f %f\n",t,x,v);


}

return 0;
}

float dxdt(float t,float x, float v)
{
return v;
}

float dvdt(float t, float x, float v)
{
return (0.5*cos(0.5*t)-1*x-0.5*pow(x,3)-0.4*v)/1;
}

int _tmain(int argc, _TCHAR* argv[])
{
wEuler=fopen("E uler.xls","w");
wHuen=fopen("He un.xls","w");
wRK=fopen("Rang e-Kutta.xls","w") ;

// char selection;
float t0,x0,v0,tn,h,t ,x,v;
int n;
// float k1,k2;
// float dydx11,dydx12,d ydx21,dydx22,sl ope1,slope2,xe, ve;
// float k11,k12,k21,k22 ,k31,k32,k41,k4 2,s1,s2;

//main:

printf("\nPleas e select the option:\n\n");
printf("======= ===========Main Menu=========== ====\n");
printf("** Option 1: Different time steps **\n");
printf("** Option 2: Same time steps **\n");
printf("** Enter EOF to end the program **\n");
printf("======= =============== =============== =====\n\n");


printf("Please Inset initial time, t0 = ");
scanf_s ("%f",&t0);
printf("Please Insert initial displacement, x0 = ");
scanf_s ("%f",&x0);
printf("Please insert initial velocity, v0= ");
scanf_s ("%f",&v0);
printf("Please insert final time,tn= ");
scanf_s ("%f",&tn);
printf("Please insert -1 to end the program.");
printf("\n");
again: printf("\nPleas e insert n value= ");
scanf_s ("%f",&n);

if(n!=-1)
{
Euler(t0,x0,v0, tn,n);
Huen(t0,x0,v0,t n,n );
RK(t0,x0,v0,tn, n);

goto again;
}


else
{
printf ("Thankyou for using.\n\n");
}

fclose(wEuler);
fclose(wHuen);
fclose(wRK);
return 0;
}

The program give me wrong answers and looping. Any advise?

[newb16]

Did you determine in which loop exactly it loops infinitely, or you'd rather want us do it for you?

[albertaw1988]

erm. it should not loop the program. it oni loop from t0 till tn (let say 0 to 100 with time steps of h) and ask the user to input another n value or -1 to end the program

i don't know what's wrong with my combined code because it seems to be correct when i try to do with 1 method.

[albertaw1988]

erm. it should not loop the program. it oni loop from t0 till tn (let say 0 to 100 with time steps of h) and ask the user to input another n value or -1 to end the program

i don't know what's wrong with my combined code because it seems to be correct when i try to do with 1 method.

[newb16]

Ok, it should not loop but it loops, so one of the loops performes endlessly. Did you find which one and why it never exits?

[albertaw1988]

there's only looping in t<tn, where t=t+h..but when the program run, it does not run the go through the h equation. the program like keep adding 0.000001 and the other values for x n v gives wrong results. I still can't figure it out.

[albertaw1988]

i think my n input gt some problem..the program should end when i input -1..but it doesn't. still can't figure out why.

[newb16]

Try to check the value of n when you calculate h, it's incorrect. And it's already incorrect when you pass it to the function.

[albertaw1988]

how would it be wrong since the individual code works when i insert n=500, it give h of 0.2, t will loop with increment of 0.2. does it mean that i have to put h function into if{}?

[newb16]

Because in scanf you have format specifier %f when reading n which is int and requires %d

[albertaw1988]

oh yeah..thanks..n ow the program runs correctly. but 1 more thing, if i enter values less than 500, some of the output gives me #INFOO and #INDOO. May I know why?