public double Function2D(double x, double y)
{
double frequency = initFrequency;
double amplitude = initAmplitude;
double sum = 0;
// octaves
for (int i = 0; i < octaves; i++)
{
sum += SmoothedNoise(x * frequency, y * frequency) * amplitude;
frequency *= 2;
amplitude *= persistence;
}
return sum;
}