Regions substraction


I have reproduced the simple experimental set-up we use and defined the related regions. Now I need to add a geometrical element (let’s call it “A”) (that I build as the intersection of 6 infinite plans (two YZP, two XZP and two PLA with the same orientation) inside another already defined bigger region (“B”).
I cannot find an easy way to simply “substract” A from B without being obliged to re-define each single zone of B (B already contains other geometrical elements ).
Can someone please help me? :slight_smile:
Many thanks in advance.


Hi @Tibe68
the easiest way to edit the regions/zones is with the geometry editor in flair please look:

  • the dedicated tutorial for that,
  • the YouTube video (is a bit old and outdated but gives clearly the concept)

Hi Vasilis,

thanks for your answer. Yes, I followed the tutorials on the official flair page and I believe I see the “building philosophy” behind. I was just wondering if it could be possible to simply apply boolean operators not only between zones but between regions too (apparently not).
All the best,


You are right, there is no possibility to subtract a region.
The only way is to subtract the whole expression inside parenthesis
+body -(....region...expression)
This is not a recommended way of working. Fluka will try to expand the parenthesis, which will exponentially grown in number of terms with respect the number of parenthesis.

Working with Zones is a bit cumbersome to setup, but offers a huge performance in the tracking.

Another option in flair is to try the experimental feature to auto-correct the regions. It is hidden in the Geometry tab in the Actions dropdown menu
Unfortunately I cannot make a screenshot when the menu is on.

There is a feature called Correct

  • Construct your inner child region and forget the overlap with the mother region
  • Once you are finished and have an overlap, click on the Correct region button, select the zone that has an overlap in one of the viewports and flair will try to autocorrect the expression of the overlap excluding from the selected region all other regions.

Note that this works well if you use infinite bodies and ONLY in the two dimensions you see on the screen. It will not correct anything that is not visible in 3rd dimension.
It could give you something that can be a good start point to further edit the zones and have a correct region.

Dear Vasilis,

thank you for the replay. Yes, the “intuitive way”
+body -(region to substract)
doesn’t work. It’s a pity because it could be very useful when you have to simulate an “evolving” experimental set-up and you change the size or the position of some stuff.
I’ve tried also the procedure you suggested using the feature Correct but without success…
So, eventually, I re-build the overall region and now it works.
All the best,


Hi @Tibe68

if you can wait for a few days, we will release a version that will be able to handle even complicated setup with parenthesis. We are currently testing it.