@tomleslie 

Thankyou. yes it works well to me as well but after deleting the 'initmesh'. So 'initmesh' is the thing which makes my program run so long?

@Preben Alsholm

Thankyou Sir for the idea and explanation. I very appreciate that. Im now trying to undertstand how your code works :) I have tried running this code and of course it works fine but my I know, is this code only valid for n=1 which is the simplest one? Because I've tried changing the value of n but there is error. The error which I may have to go back to your previoue explanation about 'Newton iteration not converging', i guess :)

@Preben Alsholm 

Thankyou Sir for the explanation. each of them really help me to understand a bit about the problem. However, may I know, as what you said above, about 'initmesh'=N. As what you can see from my code, I have already put initmesh=30000. So may I know are they two different things between your suggested initmesh and my initmesh? 

@I_Mariusz 

Thankyou so much, Sir. I have tried what u suggested and it works well (by decreasing the value of endpoint). 

Also thankyou for the explanation too :)

However, I have another doubt. Is this also the same solution if I get the 'initial Newton iteration not converging' error? Because I have others parameters to be varied and some values will give me this kind of error. I have also search other solution where maybe I need to use continuation and midpoint method. Still this idea dont manage to solve the error. Hence again, does decreasing the end point is one of the solution?

Thankyou :)

@Preben Alsholm 

Thankyou so much Sir. What a silly mistake there. And thankyou for the explanation. I appreciate that :)