Calculate Share based on Slicers

Hello,

I have created a matrix where I have the sales amount for some suppliers or brands based on some slicers. The column MAT TY represents the sales value for this year, LY for last year.

I want to create a Share for each Supplier/ Brand which should be applicable depending on the slicer. So for ex. if I select a specific Category I want to see the Share the supplier has in that category. If I select no category I want to see the Share that the supplier has in the "Group"(second slicer). I tried to put the Value for Sales(MAT TY) and show it as a percent of total column, but the problem is that if I select a specific supplier from one matrix, it changes (becomes 100% because it is calculated based on column). How can I calculate this Share in a way it can be visible when i select the supplier?

I created a Share column, but the formula is not correct. 

After that, I need to create a matrix with Value % Share change, the will contain the percent difference between this year's share and last year's share.

Thank you!