Unity crashes on play when generating texture.

Hi! Recently I have been playing around with graphics programming in unity and while attempting to create a c# script to generate a LUT unity crashes everytime I hit play ONLY when the script is enabled. I'm sure its down to dodgy programming as my c# is a bit meh. Heres the code:

 using UnityEngine;
 using System.Collections;
 
 
 public class GenerateBeckmann : MonoBehaviour {
     public int size = 64;
     private Material currentMaterial;
     public Texture2D generatedTex;
     
     float PHBeckmann(float ndoth,float m){
         float alpha = Mathf.Acos (ndoth);
         float ta = Mathf.Tan(alpha);
         float val = 1f/(m*m*Mathf.Pow(ndoth,4f)) * Mathf.Exp(-(ta * ta) / (m * m));
         return val;
     }
     private Texture2D Beckmann(){
         Texture2D beckmann = new Texture2D(size,size,TextureFormat.ARGB32,false);
         for(int i=0;i<size;i++){
             for(int j = 0;j<size;i++){
                 float val = 0.5f * Mathf.Pow(PHBeckmann(i/(float) size, j/(float)size), 0.1f);
                 beckmann.SetPixel(j, i, new Color(val,val,val,val));
             }
         }
         beckmann.Apply ();
         return beckmann;
     }
     
     // Use this for initialization
     void Start () {
         if(!currentMaterial){
             currentMaterial = transform.renderer.sharedMaterial;
             if(!currentMaterial){
                 Debug.LogWarning ("Cannot find a material on: "+transform.name);
             }
             
         }
         if(currentMaterial)
         {
             generatedTex = Beckmann ();
             currentMaterial.SetTexture ("_MainTex",generatedTex);
         }
     
     }
     
     // Update is called once per frame
     void Update () {
         
     }
 }