Is it a rational decision?

for (i = 1; i < N; i++){
    for (j = i+1; j <= N; j++){
        tg = fabs((f[j]-f[i]) / (j-i));
        if (tg > max){
            max = tg;
            imax = i;
            jmax = j;
        }
    }
}

printf("%d %d\n", imax, jmax);