How to set initial value in PersianDatePicker?

I'm using PersianDatePicker in a modal with ajax. I want to change the date of picker based on ajax response. What I did is:

$('.mydateclass').val('1399-12-12');

I also tried something like:

var pd = $('.selector').persianDatepicker();
pd.setDate(1382276091100)

but none of them worked.