Birds flying in sine wave form Unity3d

flybirds.cs

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

public class FlyBirds : MonoBehaviour {

	Vector3 firstPos;
	[SerializeField]
	Vector3 lastPos;
	[SerializeField]
	float xSpeed=5f;
	/// <summary>
	/// The distance at which the object should move up and down
	/// </summary>
	[SerializeField]
	float yLimit=50f;
	[SerializeField]
	float cosineMultiplier=2f;

	float elapsedTime;
	///Reduce to increase the wave length in y axis
	float cosineValue=0.5f;
	
	void Update () {
		elapsedTime += Time.deltaTime;
		cosineValue = Mathf.Cos( Mathf.PI  * elapsedTime * cosineMultiplier ) ; 
		Vector3 newPosition = new Vector3(lastPos.x ,(lastPos.y + yLimit) * cosineValue,lastPos.z);
		transform.position = Vector3.MoveTowards (transform.position, newPosition, xSpeed * Time.deltaTime);
	}

}