ml-agents/unity-environment/Assets/ML-Agents/Examples/Reacher/Scripts/ReacherGoal.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ReacherGoal : MonoBehaviour {

    public GameObject agent;
    public GameObject hand;
    public GameObject goalOn;

	// Use this for initialization
	void Start () {
		
	}
	
	// Update is called once per frame
	void Update () {
		
	}

    private void OnTriggerEnter(Collider other)
    {
        if (other.gameObject == hand)
        {
            goalOn.transform.localScale = new Vector3(1f, 1f, 1f);
        }
    }

    private void OnTriggerExit(Collider other)
    {
        if (other.gameObject == hand)
        {
            goalOn.transform.localScale = new Vector3(0f, 0f, 0f);
        }
    }


    private void OnTriggerStay(Collider other)
    {
        if (other.gameObject == hand)
        {
            agent.GetComponent<ReacherAgent>().reward = 0.1f;
            //agent.GetComponent<PendulumAgent>().done = true;
        }
    }
}