## Euler method in c++

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### Euler method in c++

Hi Everybody
I am beginner in c++ and I need your help plz. I implemented euler method for solving simple ODEs (y' = x -y, y(0)=1)and it is forward in time(from t=0 to t=1) and it worked well, my question is : I want to run this code backward in time(i.e. from t=1 to t=0) what i have to change in my code?
Code:
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`/* Euler for a set of first order differential equations */#include <stdio.h>#include <math.h>#define dist 0.2               /* stepsize in t*/#define MAX 1.0                /* max for t */int N=1;void euler(double x, double y[], double step); /* Euler function */double f(double x, double y[], int i);          /* function for derivatives */main(){double t, y[N];int j;y[0]=1.0;                                       /* initial condition */ for (j=0; j*dist<=MAX ;j++)                     /* time loop */{   t=j*dist;   printf("j =  %d,t = %f y[0] = %f\n", j,t, y[0]);   euler(t, y, dist);}}void euler(double x, double y[], double step){double  s[N];      /* for euler */int i;{for (i=0;i<N;i++) {     s[i]=step*f(x, y, i);}}{for (i=0;i<N;i++)      y[i]+=s[i];}}double  f(double x, double y[], int i){if (i==0) return(x-y[0]);                 /* derivative of first equation */}`

many thanks in advance!
mora78

Posts: 1
Joined: Mon May 02, 2011 7:49 am

### Re: Euler method in c++

Thanks you for sharing
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Riley103

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