source: CIVL/examples/arithmetic/diffusion.cvl

/* Commandline execution:
 *              civl verify diffusion.cvl
 */
int nx;
$input double u0[2];
int nsteps;
double kappa;
double data[3][2];
double u[2];

void init() {  
  nx = 2;
  nsteps = 2;
  kappa = 0.1;
  for (int i = 0; i < nx; i++) {
    u[i] = u0[i];
  }
}

void write(int time) {
  for (int i = 0; i < nx; i++) {
    data[time][i] = u[i];
  }
}

void update() {
        double u_new[nx];
        
        for (int i=1; i<nx-1; i++) {
          u_new[i] =  u[i] + kappa*(u[i+1] + u[i-1] - 2*u[i]);
    }
        for (int i=1; i<nx-1; i++) {
          u[i] = u_new[i];
        }
}

void main() {
        init();
        write(0);
        for (int iter = 1; iter <= nsteps; iter++) {
                update();
                write(iter);
        }
}