interface Function2D {
  float eval(float x, float y);
}

Function2D function = new Function2D() {
  float eval(float x, float y) {
    return f(x,y);
  }
};

float f(float x, float y) {
  float f;
  float sqrsum = pow(x,2) + pow(y,2);
  f = 0.2 * sqrsum -  2 * exp(-sqrsum)- exp(-(pow(x,2)+pow(y+4,2))/2);
  return f;
}