for(int i = 0; i < (steps - 1); i++)
{
    if(f.solve(lowerIntervall + delta*i) <= f.solve(lowerIntervall + delta*(i+1)))
    {
        yMax = f.solve(lowerIntervall + delta*(i+1));
    }
    else if(f.solve(lowerIntervall + delta*i) > f.solve(lowerIntervall + delta*(i+1)))
    {
        yMax = f.solve(lowerIntervall + delta*i);
    }

    if(f.solve(lowerIntervall + delta*i) <= f.solve(lowerIntervall + delta*(i+1)))
    {
        yMin = f.solve(lowerIntervall + delta*i);
    }
    else if(f.solve(lowerIntervall + delta*i) > f.solve(lowerIntervall + delta*(i+1)))
    {
        yMin = f.solve(lowerIntervall + delta*(i+1));
    }
}

// wobei delta = (upperIntervall - lowerIntervall)/(double)(steps - 1);