arduino_expo.c

const int LED[] = {9,10,11};

void setPinAndBrightnessUp (){ 
 for (double b = 2; b < 256; b = pow(b,1.15) ){
  for (int a = 0; a < 2; a++){
     analogWrite(LED[a],(int)b);
     delay(20);
     analogWrite(LED[a], 0);
     delay(10);
  }   
 }    
}
void setPinAndBrightnessDown (){ 
 for (int b = 255; b > 1; b-=5){
  for (int a = 1; a >= 0; a--){
     analogWrite(LED[a],b);
     delay(20);
     analogWrite(LED[a], 0);
     delay(10);
  }   
 }    
}
void setup() {
  pinMode( 9 , OUTPUT);
  pinMode( 10 , OUTPUT);
  pinMode( 11 , OUTPUT);
 
}

void loop() {
  setPinAndBrightnessUp();
  setPinAndBrightnessDown ();
}