Mathf.PerlinNoise not working

I am trying to make a Terrain generation based on Mathf.PerlinNoise and to set the hights i am using this code, but in the inspector all the variables are 0. Any ideas why this is the case? Thanks in advance

public float[] heights;
int num;

void Start () {
	heights = new float[100];
	num = 0;
}

void Update () {
	for(float x = 0; x <= 0.9f; x+= 0.1f)
	{
		for (float y = 0; y >= 0.9f; y += 0.1f)
		{
			heights[num] = Mathf.PerlinNoise(x,y);
		}
	}

}

Nothing to do with PerlinNoise. You are only ever assigning to the first entry in the heights array, except the inner loop isn’t running at all anyway because the condition uses >= instead of <= so actually nothing is getting assigned. After fixing the condition, put all the code in Start, make num a local variable (not actually necessary but good practice), and change heights[num] to heights[num++].