Cumulative sum of previous quarters

[#1]

Hi everybody,

I need to calculate the sum of all the previous week, for exemple if quarter 3 is selected and year 2015 is selected , i need to have the cumulative sum of quarter 1 and quarter 2 of 2015.

Here is the table in need to display:

If Quarter 3 is selected I need to have in the column " Cumul T2 Initial " The cumulative Sum of quarter 1 and quarter 2.

NB : there is a special case If Quarter 1 is selected the result must be the sum of all quarters of the last year.

Thank You for your help.